Radio communication method, radio communication system, radio communication device, and congestion control method

ABSTRACT

Disclosed is a technique to prevent a collision in a state that radio communication devices are congested. According to the technique, in the state that the radio communication devices are congested, one of the radio communication devices becomes a representative node and transmits a representative node advertisement message. When the representative node has received a data packet after transmission of the representative node advertisement message, it transmits a response confirmation message. When a radio communication device, which was not decided as the representative node, has become a normal node and received the representative node advertisement message, it transmits a data packet. Then, when receiving a confirmation message after transmission of the data packet, the radio communication device stops data packet transmission during the next active period.

TECHNICAL FIELD

The present invention relates to a radio communication method, a radiocommunication system, and a radio communication device, in which anyperiod within a superframe of a constant cycle is defined as an activeperiod and the rest is defined as a sleep period, and the active periodis divided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot.

The present invention particularly relates to low-power consumptionmedia access control (MAC) used in the case of two-way data exchangebetween radio communication devices (nodes) that move while transmittingdata periodically.

The present invention also relates to a congestion control method in aradio communication system, in which a given period within a superframeof a constant cycle is defined as an active period and the rest isdefined as a sleep period, and the active period is divided into pluraltime slots to enable each of plural radio communication devices toperform time-division two-way communication using each time slot. Thisinvention further relates to a radio communication system and a radiocommunication device.

Further, the present invention specifically relates to control ofcommunication congestion caused when radio communication devices (nodes)exist densely in a radio communication range, and to media accesscontrol for reducing the power consumption of a battery in a radiocommunication node while avoiding communication conflicts.

BACKGROUND ART

Power consumption reduction of radio hardware in radio devices is a keyrequirement. Radio communication systems include, especially asapplication examples requiring a power saving mechanism, an activeelectronic tag system, a sensor network system, etc. Since sensor nodesand the like in these active electronic tag and sensor network systemsare required to have portability and ease/flexibility of installation,they are normally battery-powered nodes with built-in small batteries.

Applications to these active electronic tag system, sensor networksystem, etc. feature low traffic. In an active electronic tag system,small data including ID (identification information) of each activeelectronic tag itself is usually transmitted. Further, in a sensornetwork system using ZigBee (registered trademark) as shown inNon-Patent Document 1, sensor nodes often perform intermittenttransmission of small sensing data.

In ZigBee (registered trademark) as shown in Non-Patent Document 1 citedbelow as a short distance wireless communication standard, a beaconsignal is used as a sync signal to define a given period within aconstant cycle as an active period (superframe period) and the rest as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot. Further,Patent Document 1 cited below as another conventional example proposes amethod of providing a reception interval immediately after a beaconsignal transmitted by each radio communication node and setting the restas a reserved period as an adhoc communication system, in which a largenumber of radio communication nodes perform asynchronous radiocommunication directly without going through another node such as a basestation or a control station. Further, Patent Document 2 cited belowproposes a method of deciding a time slot for transmitting a beaconsignal when a superframe of a constant cycle is set using, as a syncsignal, a beacon signal to be transmitted by each radio communicationnode.

In Non-Patent Document 1 enabling low-power consumption radiocommunication two techniques are defined as means for avoiding theoccurrence of a collision. The following illustrates one of thetechniques. FIG. 14 shows a procedure for detecting an empty time slotby CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) toperform transmission. In CSMA/CA, processing for confirming theavailability of radio channels is called CCA (Clear Channel Assessment).In the technique shown in FIG. 14, this CCA is performed in each timeslot, and when any node being performing radio communication isdetected, transmission is stopped, thereby making it possible to avoidthe occurrence of a collision. In the first active period AP1 (timeslots=0, 1, . . . , 7), node 1 transmits data to nodes 2 and 3 in timeslot=1, node 2 transmits data to nodes 1 and 3 in time slot=4, and node3 transmits data to nodes 1 and 2 in time slot=6. In the followingactive period AP2 (time slots=0, 1, . . . , 7), node 3 transmits data tonodes 1 and 2 in time slot=1, node 2 transmits data to nodes 1 and 3 intime slot=5, and node 1 transmits data to nodes 1 and 3 in time slot=7.

The second technique is to ensure the avoidance of occurrence of acollision in such a manner that a coordinator allocates a time slot toeach node. Non-Patent Document 1 makes it possible to have a networkstructure in which each node is placed under the control of thecoordinator responsible for building and maintenance of a network andspecification of transmission timing of each node. In this case, sinceeach node transmits data at timing instructed by the coordinator, nocollision occurs.

Further, ZigBee (registered trademark) confirms the arrival of datahaving an ACK function. If no ACK can be received, a data packet isretransmitted to improve the reliability of data packet arrival. Whenthe data packet is unicast, an ACK is transmitted without specifying thedestination immediately after completion of data reception at the datapacket destination. Only a sequence number of received data is includedin the ACK to reduce the time to create the ACK message. These twofeatures reduce the time until completion of confirming the arrival ofdata. In the case of broadcast, a node receives broadcast datatransferred by another node and determines that it is an ACK for abroadcast packet transmitted by its own node to enable confirmation ofthe arrival of data. This is called a passive ACK. Use of the passiveACK eliminates the time required to create an ACK message, and hencereduces the time until completion of confirmation of the arrival ofdata.

Patent Document 1 discloses a technique for recoding the timings of datatransmission of peripheral nodes and deciding the timing of datatransmission of its own node while avoiding a collision between datatransmission timings. This technique is a system for data exchangebetween nodes that transmit data at a constant cycle (superframe), wherea node performs a scan within the superframe before starting datatransmission to decide the timing of data transmission of its own nodewhile avoiding timings during which peripheral nodes transmit data.After that, the node continues data transmission at the timing decided.

Patent Document 2 as still another conventional example proposes amethod of providing a reception interval immediately after a beaconsignal transmitted by each radio communication node and setting the restas a reserved period as an adhoc communication system, in which a largenumber of radio communication nodes perform asynchronous radiocommunication directly without going through another node such as a basestation or a control station. Further, Patent Document 1 discloses amethod of autonomously advertising use of its own slot to an empty slotin a method of allocating each time slot to a node. According to thismethod, each node scans the time of a given time slot, and determines atime slot to be used and empty time slots to construct a table in orderto use the empty time slots sequentially, thereby enabling efficient useof time slots.

For example, if there is a node that uses no time slot any more, thetime slot is scanned as an empty time slot to be used by another node.When radio communication nodes using such a method exist densely in aradio communication range, if the number of nodes exceeds the number oftime slots, no time slot may be available and some nodes may not be ableto communicate. In such a congestion state, it is desirable that a nodethat has finished transmission should stop communication for a certainperiod of time to release its time slot so that another node can use it.In this case, considering the radio communication characteristics, it isdesirable that the node should stop transmission after confirming that aframe transmitted by itself has been delivered to a destination. In sucha case, it is considered that a receipt response (ACK, NACK) from a nodethat has received the frame is confirmed.

When a large number of radio communication nodes exist densely in aradio communication range, it is considered that communicationcongestion occurs especially in such a case that nodes using the samefrequency communicate in a time-sharing manner. Therefore, it isimportant to provide access control for avoidance of communicationconflicts. Further, in the case of nodes, such as active electronictags, which output their own information periodically using internalbatteries as power sources, collisions are controlled by shiftingtransmission timings back and forth at random in a constant cycle.However, if the node density in the radio communication range is high,collisions could disable communication. In this case, the number ofnodes to communicate is reduced until the congestion state is avoided toenable continuous communication while avoiding temporary congestion. Insuch a case, it is important to determine which node should stoptransmission.

However, if the nodes are of a type that transmits only their owninformation like active electronic tags, it is difficult to determinethe state of congestion, and there is no choice but to wait until thecongestion state is physically avoided due to the movement of the nodesor the like. Further, if the nodes are of a type that receives a commandfrom a reader like passive tags without internal batteries, the readeras a specific node manages the state and performs access control on eachtag to enable control during congestion. This is realized in such amanner that the tags perform transmission by rotation after each nodeconfirms that the reader has received information transmitted by thenode. Thus, a method of avoiding congestion is employed, in which a nodetransmitting information is notified during congestion that theinformation has been received to cause the node to stop communication inorder to reduce the number of nodes to communicate simultaneously. Theacknowledgement of information can improve the reliability ofinformation transmission. Further, since nodes stop transmission duringcongestion in order from a node that has confirmed that information wasreceived, it is considered that more efficient information transmissionis possible compared to the method in which a node that has recognizedcongestion just stops transmission for a certain period of time.

Conventional operations of sending receipt responses will be describedwith reference to FIG. 43 and FIG. 44. FIG. 43 shows an operation whenthree active-type radio communication nodes A, B, and C with internalbatteries transmit and receive unicast frames having destination nodesto which they are destined. The nodes are located in communicabledistances from one another. Although frame F1 (Dest B) destined to nodeB and output by node A can be received by nodes B and C, node B receivesit as a result of filtering of the address (Dest B) and transmits anacknowledgement (ACK 1) indicative of the reception. Further, as forframe 2 (Dest C) destined to node C and output by node B, anacknowledgement is made by ACK 2 from node C. Here, transmission of anew acknowledgement frame during congestion increases the number offrames necessary to be transmitted, and could increase congestion aswell. Therefore, in Non-Patent Document 1 or the like, an ACK frame isimmediately returned in a very short frame unlike data frames F1 and F2.Such a method enables receipt notification to nodes A and B that sentframes F1 and F2 without increasing congestion and adding detailedinformation for specifying a frame in which ACK is being returned.

However, in such a unicast case that a destination is thus decided,since the number of nodes to respond is one, nodes B and C that havereceived frames F1 and F2, respectively, can immediately return ACKframes (ACK1, ACK2). However, as for frames to be transmitted to anindefinite number of nodes in the case of broadcast or the like, ifplural nodes return ACKs upon reception, an ACK collision occurs andthis makes it difficult to confirm reception. Therefore, in PatentDocument 2 or the like, such a passive ACK method that confirmsresponses in response to a returned frame transmitted by itself as shownin FIG. 43 where received frames F11, F12, and F13 are transferred.

Non-Patent Document 1: IEEE802.15.4

Patent Document 1: Japanese Patent Application Publication No.2006-121332 (Abstract)

Patent Document 2: Japanese Patent Application Publication No.2004-228926 (FIG. 2)

DISCLOSURE OF THE INVENTION Problems to be Solved by First and SecondInventions

However, the above-mentioned techniques are not always applicable to acase where nodes are congested in a communication system in which movingcommunication nodes carry out two-way data exchange. The first techniquein Non-Patent Document 1 enables transmission by distributed controlbecause the transmission timing is selected depending on the randomnessof each node. However, if the number of nodes existing in a mutualpropagation coverage is twice as many as the number of time slots in oneactive period, communication may be totally disabled. If sets of twonodes that have performed CCA at the same timing in the same time slotexist as many as the number of time slots, nodes communicable in thisactive period are unable to exist. This means that, as the number ofnodes congested in the same radio propagation coverage increases, thechances to make communication impossible increase.

The second technique in Non-Patent Document 1 guarantees transmissionpaths, so that nodes allocated time slots from a coordinator cantransmit data reliably. However, this guaranteed feature is limited to acase where the network topology is of a star type with the coordinatoras its center. In a communication system in which node position cannotbe fixed because nodes move, a node having a specific function as thecoordinator cannot be always held in close proximity to other nodes.Further, even if the coordinator always exists close to mobile nodes, itis very difficult to build a star topology in the communication systemin which nodes move. The problem is that data transmission cannot bestarted unless a collision in control data exchange for forming a startopology can be avoided.

Further, a time slot has to be allocated from the coordinator each timedata is transmitted. This also poses a problem that data transmissioncannot be started unless a collision in data exchange for causing amobile node to be allocated a time slot can be avoided.

If nodes that move while transmitting data periodically are congested,use of the ACK function of ZigBee (registered trademark) is madedifficult. In the case of unicast, a node as a destination described ina data packet transmits an ACK to confirm the arrival of data. However,in a system having no destination information in a data packet, such asan electronic tag system, since a node to transmit the ACK cannot bespecified from plural nodes that have received the data packet, the ACKcannot be transmitted. If all the nodes that have received the datapacket transmit the ACK without specifying a node to transmit the ACK, atransmission collision occurs. In the case of broadcast, a passive ACKneeds to be received from other nodes. However, in a system, such as theelectronic tag system, in which no data packet is transferred, receptionof the passive ACK cannot be expected. Therefore, in such a state thatmobile nodes are congested, each node cannot confirm the arrival of datatransmitted by itself using the ACK function of ZigBee (registeredtrademark).

In the technique of Patent Document 1, as the number of nodes totransmit data continues to increase, available transmission timings in asuperframe is reduced, and this makes some nodes unable to transmitdata. Further, nodes that have scanned and selected the sametransmission timing always cause a transmission collision after that.Thus, when moving nodes are gathered and hence the density of nodes inthe communicable range increases, the opportunity of transmission to anode waiting for a data transmission request is reduced. Further, evenif a transmission collision repeatedly occurs, there is no scheme tochange the transmission timing, and this makes it impossible to have anopportunity of retransmission of data that has caused a reception error.

Further, when a traffic intersection, a train, a place of refuge in adisaster area, etc. are crowded with people who are carrying mobilenodes and hence the mobile nodes are congested, if data exchange isperformed among them, the transmission timing may be the same, causing aproblem that the possibility of occurrence of a data transmission errorincreases.

Problems to be Solved by Third Invention

In the case of use of such a method that achieves power saving of a nodewith a built-in battery, in which a superframe is formed of given timeslots in time-division multiplexing two-way communications usingtime-slot synchronization type TDMA (Time Division Multiple Access) anda sleep period is provided in the superframe period by achievingsynchronization in superframes, when the number of nodes existing in acommunication range is smaller than the number of time slots in a givensuperframe, radio needs to remain receivable for empty time slots thatmay sleep, posing a problem with power saving.

Even when a method for self-sustained empty slot management as describedin Patent Document 1 is employed, if communication nodes involvemovement and frequently change time slots used, there is a need to scanall given time slots in order to grasp their usage status, so thatfrequent scans of time slots are required, thereby making it difficultto achieve power saving.

Problems to be Solved by Fourth Invention

Upon response confirmation using a passive ACK for the above-mentionedbroadcast case, a frame transmitted by a node needs to be transferredsequentially. When a frame as large as data transmitted is used and alarge number of nodes perform broadcast communication, not onlycongestion is increased, but also response confirmation cannot be made,for example, on such a network that does not transfer broadcast frames.

OBJECTS OF INVENTIONS

In view of the above conventional problems, it is an object of the firstinvention to provide a radio communication method, a radio communicationsystem, and a radio communication device, capable of preventing acollision in such a state that radio communication devices arecongested.

In view of the above conventional problems, it is an object of thesecond invention to provide a radio communication method, a radiocommunication system, and a radio communication device, capable ofautonomously increasing transmission opportunities when a collisionoccurs in such a state that mobile nodes with low power consumption arecongested, and capable of increasing the number of nodes that stoptransmission to reduce the number of nodes that attempt transmission ata time.

It is an object of the third invention to provide a radio communicationmethod, a radio communication system, and a radio communication device,capable of operating with an appropriate number of time slots in radiocommunication, where a radio communication device advertises its owninformation to an unspecified number of radio communication devices thatinvolve movement, and hence capable of achieving power saving.

It is an object of the fourth invention to provide a congestion controlmethod, a radio communication system, and a radio communication device,capable of autonomously stopping transmission using receipt responseinformation that does not increase congestion during a period ofcongestion in radio communication, where a radio communication deviceadvertises its own information to an unspecified number of radiocommunication devices, and capable of autonomously determining theelimination of a congestion state to resume transmission.

<First Invention>

In order to attain the above object, according to the first invention,there is provided a radio communication method, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the method comprising:

a step of allowing each of the plural radio communication devices todetect, based on the communication condition in each time slot, such astate that plural radio communication devices are congested, and todecide one of the plural radio communication devices as a representativenode;

a step of allowing a first radio communication device decided as therepresentative node to transmit a representative node advertisementmessage advertising that the first radio communication device becomesthe representative node;

a step of allowing a second radio communication device, which has notbeen decided as the representative node, to transmit a data packet whenreceiving the representative node advertisement message;

a step of allowing the first radio communication device to transmit aconfirmation message when receiving the data packet after transmittingthe representative node advertisement message; and

a step of allowing the second radio communication device to stop datapacket transmission during the next active period when receiving theconfirmation message after transmitting the data packet.

This structure makes it possible to prevent a collision in such a statethat radio communication devices are congested.

In order to attain the above object, according to the first invention,there is also provided a radio communication system, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising:

means for allowing each of the plural radio communication devices todetect, based on the communication condition in each time slot, such astate that plural radio communication devices are congested, and todecide one of the plural radio communication devices as a representativenode;

means for allowing a first radio communication device decided as therepresentative node to transmit a representative node advertisementmessage advertising that the first radio communication device becomesthe representative node;

means for allowing a second radio communication device, which has notbeen decided as the representative node, to transmit a data packet whenreceiving the representative node advertisement message;

means for allowing the first radio communication device to transmit aconfirmation message when receiving the data packet after transmittingthe representative node advertisement message; and

means for allowing the second radio communication device to stop datapacket transmission during the next active period when receiving theconfirmation message after transmitting the data packet.

This structure makes it possible to prevent a collision in such a statethat radio communication devices are congested.

In order to attain the above object, according to the first invention,there is further provided a radio communication device in a radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and the rest is defined asa sleep period, and the active period is divided into plural time slotsto enable each of plural radio communication device to performtime-division two-way communication using each time slot, the devicecomprising:

means for detecting, based on the communication condition in each timeslot, such a state that plural radio communication devices arecongested, and deciding one of the plural radio communication device asa representative node;

means for transmitting a representative node advertisement messageadvertising that the radio communication device becomes therepresentative node when having been decided as the representative node;

means for transmitting a confirmation message when receiving a datapacket after transmitting the representative node advertisement message;and

means which, if having not been decided as the representative node,transmits a data packet when receiving the representative nodeadvertisement message, and stops data packet transmission during thenext active period when receiving the confirmation message aftertransmitting the data packet.

This structure makes it possible to prevent a collision in such a statethat radio communication devices are congested.

The structure may be such that, when the data packet is not receivedafter the confirmation message is transmitted, or when the number ofcollision detecting time slots is equal to or less than a referencevalue, transmission of the representative node advertisement message isstopped during the next active period, and when the representative nodeadvertisement message is not received after data packet transmission isstopped, data packet transmission is resumed during the next activeperiod.

This structure makes it possible to resume data packet transmission whenthe congested state of the radio communication devices is eliminated.

The structure may also be such that, when the representative node isdecided, such a state that plural radio communication devices arecongested is detected based on the communication condition in each timeslot, a representative node candidate declaration message declaring thatthe radio communication device becomes a representative node candidateis transmitted during the next active period, the representative nodecandidate declaration message is received, and based on a predeterminedmethod, one of the plural radio communication devices is decided as therepresentative node.

This structure makes it easy to decide the representative node.

The structure may further be such that, when the radio communicationdevice decided as the representative node stops transmission of therepresentative node advertisement message, the priority of becoming arepresentative node candidate next time is reduced.

This structure makes it possible to prevent some radio communicationdevices from often becoming the representative node and hence becomingimpossible to transmit their data packets.

<Second Invention>

In order to attain the above object, according to the second invention,there is provided a radio communication method, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication device to perform time-division two-way communicationusing each time slot, the method comprising:

a step of allowing each of the plural radio communication devices todetect a collision in each time slot; and

a step of allowing each of the plural radio communication device notonly to transmit a collision advertisement message to a predeterminedtime slot of the plural time slots of the next active period but also toextend the next active period when the radio communication device hasdetected the collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

In order to attain the above object, according to the second invention,there is also provided a radio communication method, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the method comprising:

a step of allowing each of the plural radio communication device todetect a collision in each time slot; and

a step of allowing each of the plural radio communication device notonly to extend the current active period but also to transmit acollision advertisement message to a predetermined time slot of thecurrent active period when the radio communication device has detectedthe collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

In order to attain the above object, according to the second invention,there is provided a radio communication system, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising:

means for allowing each of the plural radio communication device todetect a collision in each time slot; and

means for allowing each of the plural radio communication device notonly to transmit a collision advertisement message to a predeterminedtime slot of the plural time slots of the next active period but also toextend the next active period when the radio communication device hasdetected the collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

In order to attain the above object, according to the second invention,there is also provided a radio communication system, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising:

means for allowing each of the plural radio communication device todetect a collision in each time slot; and

means for allowing each of the plural radio communication device notonly to extend the current active period but also to transmit acollision advertisement message to a predetermined time slot of thecurrent active period when the radio communication device has detectedthe collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

In order to attain the above object, according to the second invention,there is provided a radio communication device in a radio communicationsystem, in which any period within a superframe of a constant cycle isdefined as an active period and the rest is defined as a sleep period,and the active period is divided into plural time slots to enable eachof plural radio communication devices to perform time-division two-waycommunication using each time slot, the device comprising:

means for detecting a collision in each time slot; and

means for not only transmitting a collision advertisement message to apredetermined time slot of the plural time slots of the next activeperiod but also extending the next active period when the radiocommunication device has detected the collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

In order to attain the above object, according to the second invention,there is also provided a radio communication device in a radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and the rest is defined asa sleep period, and the active period is divided into plural time slotsto enable each of plural radio communication devices to performtime-division two-way communication using each time slot, the devicecomprising:

means for detecting a collision in each time slot; and

means for not only extending the current active period but alsotransmitting a collision advertisement message to a predetermined timeslot of the current active period when the radio communication devicehas detected the collision.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

The structure may be such that the radio communication device that hasdetected the collision transmits the collision advertisement messagetogether with data to another time slot for transmitting the data duringthe current active period as well as to the predetermined time slot.

This structure makes it possible to autonomously increase theopportunity of transmission when a collision occurs in such a state thatradio communication devices are congested.

The structure may also be such that

the collision advertisement message includes time slot identificationinformation indicative of the time slot that has detected the collision,and

each of the plural radio communication devices that have received thecollision advertisement message stops next transmission when a time slottransmitted by itself last time does not match the time slotidentification information in the collision advertisement message.

This structure makes it possible to increase the number of nodes thatstop transmission in order to reduce the number of nodes that attempttransmission at a time.

<Third Invention>

In order to attain the above object, according to the third invention,there is provided a radio communication method, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the method comprising:

a step of allowing each of the plural radio communication devices totransmit a frame including a field of receipt response information on aframe received from another radio communication device in each of theplural time slots during each time slot period; and

a step of allowing each of the plural radio communication devices thathave received the frame to increase or decrease the number of time slotsused by its own device during the next superframe period based on eachpiece of receipt response information in the field of the receiptresponse information within the previous superframe period.

This structure makes it possible to operate with an appropriate numberof time slots and hence to achieve power saving.

The structure may be such that

when each of the plural radio communication devices was not able totransmit a frame, its own device further transmits a flag indicativethereof in a frame to be transmitted next, and

each of the plural radio communication devices that have received theframe increases the number of time slots used by its own device by thenumber of flags within the frame.

The structure may also be such that, when the receipt responseinformation contains error information, the number of time slots used isincreased by the number of pieces of error information.

This structure makes it possible to increase, in a stroke, the number oftime slots that are in short supply.

In order to attain the above object, according to the third invention,there is also provided a radio communication system, in which any periodwithin a superframe of a constant cycle is defined as an active periodand the rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising:

means for allowing each of the plural radio communication devices totransmit a frame including a field of receipt response information on aframe received from another radio communication device in each of theplural time slots during each time slot period; and

means for allowing each of the plural radio communication devices thathave received the frame to increase or decrease the number of time slotsused by its own device during the next superframe period based on eachpiece of receipt response information in the field of the receiptresponse information within the previous superframe period.

This structure makes it possible to operate with a suitable number ofslots and hence to achieve power saving.

The structure may be such that

when each of the plural radio communication devices was not able totransmit a frame, its own device further transmits a flag indicativethereof in a frame to be transmitted next, and

each of the plural radio communication devices that have received theframe increases the number of time slots used by its own device by thenumber of flags within the frame.

This structure makes it possible to increase, in a stroke, the number oftime slots that are in short supply.

In order to attain the above object, according to the third invention,there is further provided a radio communication device in a radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and the rest is defined asa sleep period, and the active period is divided into plural time slotsto enable each of plural radio communication devices to performtime-division two-way communication using each time slot, the devicecomprising:

means for transmitting a frame including a field of receipt responseinformation on a frame received from another radio communication devicein each of the plural time slots during each time slot period; and

means which, when having received the frame, increases or decreases thenumber of time slots used by its own device during the next superframeperiod based on each piece of receipt response information in the fieldof the receipt response information within the previous superframeperiod.

This structure makes it possible to operate with an appropriate numberof time slots and hence to achieve power saving.

The structure may be such that the radio communication device furthercomprising:

means which, when its own device was not able to transmit a frame,transmits a flag indicative thereof in a frame to be transmitted next,and

means which, when having received the frame, increases the number oftime slots used by its own device by the number of flags within theframe.

This structure makes it possible to increase, in a stroke, the number oftime slots that are in short supply.

<Fourth Invention>

In order to attain the above object, according to the fourth invention,there is provided a congestion control method in a radio communicationsystem, in which any period within a superframe of a constant cycle isdefined as an active period and the rest is defined as a sleep period,and the active period is divided into plural time slots to enable eachof plural radio communication devices to perform time-division two-waycommunication using each time slot, the method comprising:

a step of allowing each of the plural radio communication devices totransmit a frame including a field of receipt response information on aframe received from another radio communication device in each of theplural time slots during each time slot period; and

a step of allowing each of the plural radio communication devices thathave received the frame to determine whether to stop transmission of itsown device during the next superframe period based on each piece ofreceipt response information in the field of the receipt responseinformation within the previous superframe period.

This structure makes it possible to broadcast, during each superframeperiod, receipt response information on a frame received from each ofplural radio communication devices during each time slot period in orderto determine whether to stop transmission of its own device during thenext superframe period.

The structure may be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

in the determination step, it is determined whether the total number ofpieces of information of “successful reception” and “error reception” inthe field of the receipt response information within the previoussuperframe period exceeds a first threshold value to determine whetherto stop transmission of its own device during the next superframeperiod.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may also be such that the receipt response informationconsists of information indicative of “no reception,” “successfulreception,” or “error reception,” and

in the determination step, it is determined whether the number of piecesof information of “successful reception” in the field of the receiptresponse information within the previous superframe period exceeds asecond threshold value to determine whether to stop transmission of itsown device during the next superframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may further be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

in the determination step, it is determined whether the number of piecesof information of “successful reception” for a time slot used by its ownnode in the field of the receipt response information within theprevious superframe period exceeds a third threshold value to determinewhether to stop transmission of its own device during the nextsuperframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

Further, the structure may be such that

when having stopped transmission of its own node in the determinationstep, it is determined whether to resume transmission of its own deviceduring the next superframe period based on each piece of receiptresponse information in the field of the receipt response informationwithin the previous superframe period.

This structure makes it possible to determine whether to resumetransmission of its own device during the next superframe period.

In order to attain the above object, according to the fourth invention,there is also provided a radio communication system, in which any periodwithin a superframe of a constant cycle is defined as an active periodand rest is defined as a sleep period, and the active period is dividedinto plural time slots to enable each of plural radio communicationdevices to perform time-division two-way communication using each timeslot, the system comprising:

means for allowing each of the plural radio communication devices totransmit a frame including a field of receipt response information on aframe received from another radio communication device in each of theplural time slots during each time slot period; and

means for allowing each of the plural radio communication devices thathave received the frame to determine whether to stop transmission of itsown device during the next superframe period based on each piece ofreceipt response information in the field of the receipt responseinformation within previous superframe period.

This structure makes it possible to broadcast, during each superframeperiod, receipt response information on a frame received from each ofplural radio communication devices during each time slot period in orderto determine whether to stop transmission of its own device during thenext superframe period.

The structure may be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the total number of pieces ofinformation of “successful reception” and “error reception” in the fieldof the receipt response information within the previous superframeperiod exceeds a first threshold value to determine whether to stoptransmission of its own device during the next superframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may also be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the number of pieces ofinformation of “successful reception” in the field of the receiptresponse information within the previous superframe period exceeds asecond threshold value to determine whether to stop transmission of itsown device during the next superframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may further be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the number of pieces ofinformation of “successful reception” for a time slot used by its ownnode in the field of the receipt response information within theprevious superframe period exceeds a third threshold value to determinewhether to stop transmission of its own device during the nextsuperframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

Further, the structure may be such that

when having stopped transmission of its own node, the determinationmeans determines whether to resume transmission of its own device duringthe next superframe period based on each piece of receipt responseinformation in the field of the receipt response information within theprevious superframe period.

This structure makes it possible to determine whether to resumetransmission of its own device during the next superframe period.

In order to attain the above object, according to the fourth invention,there is further provided a radio communication device in a radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the devicecomprising:

means for transmitting a frame including a field of receipt responseinformation on a frame received from another radio communication devicein each of the plural time slots during each time slot period; and

means which, when having received the frame, determines whether to stoptransmission of its own device during the next superframe period basedon each piece of receipt response information in the field of thereceipt response information within the previous superframe period.

This structure makes it possible to broadcast, during each superframeperiod, receipt response information on a frame received from each ofplural radio communication devices during each time slot period in orderto determine whether to stop transmission of its own device during thenext superframe period.

The structure may be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the total number of pieces ofinformation of “successful reception” and “error reception” in the fieldof the receipt response information within the previous superframeperiod exceeds a first threshold value to determine whether to stoptransmission of its own device during the next superframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may also be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the number of pieces ofinformation of “successful reception” in the field of the receiptresponse information within the previous superframe period exceeds asecond threshold value to determine whether to stop transmission of itsown device during the next superframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

The structure may further be such that

the receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and

the determination means determines whether the number of pieces ofinformation of “successful reception” for a time slot used by its ownnode in the field of the receipt response information within theprevious superframe period exceeds a third threshold value to determinewhether to stop transmission of its own device during the nextsuperframe period.

This structure makes it possible to determine whether to stoptransmission of its own device during the next superframe period.

Further, the structure may be such that

when having stopped transmission of its own node, the determinationmeans determines whether to resume transmission of its own device duringthe next superframe period based on each piece of receipt responseinformation in the field of the receipt response information within theprevious superframe period.

This structure makes it possible to determine whether to resumetransmission of its own device during the next superframe period.

EFFECTS OF INVENTIONS

According to the first invention, when the frequency of occurrence oftransmission collisions in such a state that mobile nodes with low powerconsumption are congested increases to reduce the rate of data packetreachability, a node can confirm the presence of nodes that havereceived a data packet transmitted by its own node. Further, a node thatwas able to confirm the delivery of a data packet to peripheral nodestemporarily stops data transmission, and this can reduce the number ofnodes that attempt to use the same time slot. Thus, the success rate ofdata packet transmission can be increased while acknowledging the datapacket.

According to the second invention, when a collision has occurred in sucha state that mobile nodes with low power consumption are congested,transmission opportunities can be autonomously increased. The number ofnodes that stop transmission is also increased, and this can reduce thenumber of nodes that attempt transmission at a time. As a result, nodesare allowed to autonomously have more transmission opportunities,increasing the success rate of data packet transmission even in such astate that the nodes are congested. Further, nodes can haveopportunities to retransmit data that has not received due to atransmission collision.

According to the third invention, a node estimates the number of nodesexisting around it using efficient receipt response information fromplural nodes to operate with a limited number of time slots in radiocommunication, where the node advertises its own information to anunspecified number of radio communication devices (nodes). This makes itpossible to reduce power consumption without using unnecessary timeslots during communication among fewer nodes. Further, the node isprovided with a flag bit in a field of receipt response to indicate thatit was not able to transmit, and this allows the node to know how manytime slots are in short supply, making it possible to increase thenumber of time slots efficiently.

According to the fourth invention, it is possible for a node to stop andresume transmission autonomously using efficient receipt responseinformation from plural nodes in radio communication, where the nodeadvertises its own information to an unspecified number of radiocommunication devices (nodes). This makes it possible for nodes havingthe same function alone to autonomously avoid congestion, eliminatingthe need to use a specific control node separately. Further, receiptresponses from plural nodes are set as receipt responses for time slots,and this makes it possible to reduce the amount of additionalinformation for receipt responses, eliminating the increase in theamount of transmitted data. Further, the node stops transmission afterconfirming, using the receipt responses from the plural nodes, receptionof a frame transmitted by its own node, and this makes it possible tostop transmission with assurance that there are nodes that have receivedthe frame transmitted by its own node. In addition, it is possible todetermine a congestion state from information included in a few framesreceived in time-division multiplexing communications that build pluraltime slots. In this case, there is no need to receive all time slots inorder to determine congestion, and this makes it possible to reducepower consumption during congestion.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] It is an explanatory diagram showing state transition in aradio communication method, a radio communication system, and a radiocommunication device according to the first invention.

[FIG. 2] It is an explanatory diagram showing a structure example oftime slots in the first invention.

[FIG. 3] It is an explanatory diagram showing an example of a controlmessage format in the first invention.

[FIG. 4] It is a flowchart for explaining the operation of a firstembodiment when the radio communication device according to the firstinvention is a representative node candidate.

[FIG. 5] It is a flowchart for explaining the details of packetreception processing of FIG. 4.

[FIG. 6] It is a flowchart for explaining the operation of the firstembodiment when the radio communication device according to the firstinvention is a normal node.

[FIG. 7] It is an explanatory diagram showing an operation example ofthe first embodiment of the first invention.

[FIG. 8] It is an explanatory diagram showing the operation example ofthe first embodiment of the first invention.

[FIG. 9] It is a flowchart for explaining the operation of a secondembodiment when the radio communication device according to the firstinvention is a representative node candidate.

[FIG. 10] It is a flowchart for explaining the operation of the firstembodiment when the radio communication device according to the firstinvention is a normal node.

[FIG. 11] It is an explanatory diagram showing an operation example ofthe second embodiment of the first invention.

[FIG. 12] It is an explanatory diagram showing the operation example ofthe second embodiment of the first invention.

[FIG. 13] It is a block diagram showing the first and second embodimentsof the radio communication device according to the first invention.

[FIG. 14] It is an explanatory diagram showing, as one of conventionaltechniques, a procedure for detecting an empty time slot by CSMA/CA toperform transmission.

[FIG. 15] It is an explanatory diagram showing the structure of timeslots in a radio communication method, a radio communication system, anda radio communication device according to the second invention.

[FIG. 16] It is an explanatory diagram showing the structure of acollision advertisement message in the second invention.

[FIG. 17] It is a flowchart for explaining the operation of a firstembodiment of the radio communication device according to the secondinvention.

[FIG. 18] It is a flowchart for explaining the details of packetreception processing of FIG. 17.

[FIG. 19] It is a flowchart for explaining the details of extensioncontrol processing of FIG. 17.

[FIG. 20] It is an explanatory diagram showing an operation example ofthe first embodiment of the second invention.

[FIG. 21] It is a flowchart for explaining the operation of a secondembodiment of the radio communication device according to the secondinvention.

[FIG. 22] It is a flowchart for explaining the details of packetreception processing of FIG. 21.

[FIG. 23] It is a flowchart for explaining the details of extensioncontrol processing of FIG. 21.

[FIG. 24] It is an explanatory diagram showing an operation example ofthe second embodiment of the second invention.

[FIG. 25] It is a block diagram showing the first and second embodimentsof the radio communication device according to the second invention.

[FIG. 26] It is a diagram for explaining radio node classification andthe structure of a system in an embodiment of the third invention.

[FIG. 27] It is an explanatory diagram showing a superframe period andthe structure of time slots in the embodiment of the third invention.

[FIG. 28] It is an explanatory diagram showing an operation sequence ofresponse confirmation in the embodiment of the third invention.

[FIG. 29] It is a block diagram showing the structure of a radiocommunication node in the embodiment of the third invention.

[FIG. 30] It is a block diagram showing the details of the configurationof a control section of FIG. 29.

[FIG. 31] It is an explanatory diagram showing the structure of a framein the embodiment of the third invention.

[FIG. 32] It is a flowchart for explaining the operation of an ACKgeneration section in the embodiment of the third invention.

[FIG. 33] It is a flowchart for explaining the operation of a number ofslots controlling section of FIG. 30.

[FIG. 34] It is an explanatory diagram showing the structure of a framein an embodiment of the fourth invention.

[FIG. 35] It is an explanatory diagram showing ACK field generationtiming in the embodiment of the fourth invention.

[FIG. 36] It is an explanatory diagram showing a response confirmationmethod using an ACK field in the embodiment of the fourth invention.

[FIG. 37] It is a block diagram showing the structure of a radiocommunication node in the embodiment of the fourth invention.

[FIG. 38] It is a block diagram showing in detail the configuration of acontrol section of the radio communication node in the embodiment of thefourth invention.

[FIG. 39] It is a flowchart for explaining processing in a congestioncontrol section of FIG. 38.

[FIG. 40] It is a flowchart for explaining the details ofstop-of-transmission determination processing of FIG. 39.

[FIG. 41] It is a flowchart for explaining the details ofreturn-to-transmission determination processing of FIG. 39.

[FIG. 42] It is a diagram for explaining a sequence of controloperations during congestion in the embodiment of the fourth invention.

[FIG. 43] It is a diagram for explaining the operation of receiptresponses to unicast frames in a conventional system.

[FIG. 44] It is a diagram for explaining the operation of receiptresponses to broadcast frames in the conventional system.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

<First Invention>

FIG. 1 is an explanatory diagram showing state transition in a radiocommunication method, a radio communication system, and a radiocommunication device according to the first invention. FIG. 1( a) showsthat Node 1 and Node 2 are located in a range communicable with eachother, Node 2 and Node 3 are located in a range communicable with eachother, and Node 1 and Node 3 are not located in a range communicablewith each other. In this case, the state of Node 2 makes transition to arepresentative node (DesiGnated Node and hereinafter DGN) as shown inFIG. 1( b) in this invention. Here, the states of FIG. 1( a) and FIG. 1(b) are called Spare Mode and Dense Mode, respectively.

In the first invention, any period within a superframe of a constantcycle is defined as an active period and the rest is defined as a sleep(inactive) period, and the active period is divided into plural timeslots (=0, 1, . . . , 7) as shown in FIG. 2. When each of plural radiocommunication devices (nodes) uses each time slot to performtime-division two-way communication, the first time slot=0 is defined asan administrative slot, and subsequent time slots=1 to 7 are defined asdata transmission slots (=1 to 7) and control slots (=1-7),respectively. The administrative slot (=0) lets the DGN transmit a DGNadvertisement message and allows a collision. The data transmissionslots (=1-7) are selected at random by nodes (normal nodes), which didnot become the DGN, to transmit data (packets). When receiving data inany of the data transmission slots (=1-7), the DGN transmits aconfirmation message (ACK) in the immediately following control slot(=1-7). Further, the DGN selects a control slot (=1-7) at random totransmit a control packet.

FIG. 3 shows an example of a control message format, which consists ofthe kind of message (Type) and the node ID of each transmission source.Type indicates the following kinds of messages.

00: CDGN (Candidate for DGN, i.e., candidate for representative node)declaration message

01: DGN advertisement message

10: ACK

First Embodiment of First Invention

FIG. 4 and FIG. 5 are flowcharts for explaining the operation of acandidate for a representative node (CDGN) according to a firstembodiment. In FIG. 4, it is first judged whether transition to DenseMode (DM) is made by CSMA/CD according to the time slot duty cycle (notethat “time slot” is simply referred to as “slot” in the drawing) and thecollision rate of time slots, and a node concerned becomes a CDGN (stepsS1 and S2). If it does not become the CDGN, it makes transition to anormal node (step S3), and processing ends. On the other hand, if it isjudged that the node becomes the CDGN, a CDGN declaration message isgenerated (step S4), and a control slot (=1-7) for transmitting the CDGNdeclaration message is decided (step S5). It is then judged whether thetiming of the time slot is a control slot for transmitting the CDGNdeclaration message (step S6), and if so, the CDGN declaration messageis transmitted (step S7). On the other hand, if not, receptionprocessing shown in detail in FIG. 5 is performed (step S8). In thereception processing of step S8, as shown in detail in FIG. 5, it isjudged whether a received packet is a CDGN declaration message (stepS31), and if so, the CDGN declaration message is recorded (step S32). Onthe other hand, if not, the received packet is processed as a datapacket (step S33).

Returning to FIG. 4, it is judged in step S9 whether it is the finalslot (=7), and if not, processing returns to step S6. On the other hand,if so, processing proceeds to step S10, and a DGN is decided by apredetermined method (to be described later) from received (andtransmitted) CDGN declaration messages. It is then judged whether itsown node becomes the DGN (step S11). If it does not become the DGN, theCDGN makes transition to a normal node in Dense Mode (DM) (step S12),and processing ends. On the other hand, if it becomes the DGN, a DGNadvertisement message is generated (step S13), and the DGN advertisementmessage is transmitted in time slot=0 of the next active period (stepS14). It is then determined whether a data packet has been received(step S15), and if it has been received, an ACK is transmitted in thecontrol slot in which the data packet was received (step S16). It isthen determined whether it is the final time slot=7 (step S17). If not,processing returns to step S15, while if so, processing proceeds to stepS18.

It is determined in step S18 whether no data packet has been receivedduring the active period. If any data packet has been received,processing returns to step S14 to continue the operation as the DGN,while if not received, processing proceeds to step S19. In step S19,transmission of the DGN advertisement message is stopped during the nextactive period, and then, a time slot for transmitting a data packetduring the next active period is decided (step S20). Since no datapacket is transmitted from its own node during DM, a time slot fortransmitting a data packet is decided in step S20. It is then determinedwhether it is the timing of the transmission time slot for its own node(step S21). If so, a data packet is transmitted (step S22), while ifnot, the reception processing shown in detail in FIG. 5 is performed(step S23). It is then determined whether it is the final time slot=7(step S24). If not, processing returns to step S21, while if so,processing proceeds to step S25. In step S25, the priority of becoming aCDGN at the next opportunity to enter Dense Mode (DM) is reduced. Then,DM is terminated (step S26), and this processing ends.

Processing performed by a normal node will next be described withreference to FIG. 6. First, a time slot for transmitting a data packetis decided (step S41). It is then determined whether it is the timing ofthe time slot for its own node to transmit a data packet (step S42). Ifso, the data packet is transmitted (step S43), while if not, thereception processing shown in detail in FIG. 5 is performed (step S44).It is then determined whether it is the final time slot (step S45). Ifnot, processing returns to step S42, while if so, processing proceeds tostep S46.

It is determined in step S46 whether a CDGN declaration message has beenreceived in a control slot. If not received, processing returns to stepS41, while if received, a DGN (another node) is decided by apredetermined method (to be described later) from the received CDGNdeclaration message (step S47). After that, the state of the normal nodemakes transition from SM to DM. It is then determined whether datapacket transmission is being stopped (step S48). If being stopped, thereception processing shown in detail in FIG. 5 is performed (step S49),and processing proceeds to step S56. On the other hand, if packettransmission is not being stopped in step S48, a time slot fortransmitting a data packet is decided (step S50), and it is thendetermined whether the timing of the time slot is for its own node totransmit a data packet (step S51). If so, the data packet is transmitted(step S52), and it is then determined whether an ACK message has beenreceived in a control slot (step S53). If so, transmission of the datapacket is stopped (step S54), and processing proceeds to step S56. Onthe other hand, if no ACK message has been received in step S53,processing proceeds to step S56 without stopping transmission of thedata packet. In step S51, if it is not the time slot for data packettransmission, the reception processing shown in detail in FIG. 5 isperformed (step S55), and processing proceeds to step S56.

It is determined in step S56 whether it is the final time slot. If not,processing returns to step S48, while if so, processing proceeds to stepS57. It is determined in step S57 whether a DGN advertisement messagehas been received in time slot=0 or a collision has been detected intime slot=0. If either of them is determined, processing returns to stepS48 to continue DM, while if none of them is determined, data packettransmission is resumed (step S58), and processing returns to step S41.At this time, the normal node exits DM and its state makes transition toSM.

FIG. 7 and FIG. 8 show an example operation of nodes 1, 2, and 3according to the first embodiment of the first invention. Here, due tolimitations of space, FIG. 7 shows active periods AP1 and AP2, and FIG.8 shows active periods AP3 and AP4.

<Active Period AP1>

(1) Node 1 that detected a collision during the previous active periodand decided transition to CDGN transmits a CDGN declaration message incontrol slot=1 of active period AP1,

(2) node 3 that detected no collision during the previous active periodtransmits a data packet in data transmission slot=4 of active periodAP1, and

(3) node 2 that detected a collision during the previous active periodand decided transition to CDGN transmits a CDGN declaration message incontrol slot=7 of active period AP1.

(4)(5)(6) Nodes 1, 2, 3 select a representative node (DGN) by apredetermined method (for example, node having the smallest node ID)from received or transmitted CDGN declaration messages. Here, Node 1having the smallest node ID is selected. Here, node 2 that have turnedinto CDGN makes transition to a normal node (steps S10 to S12 in FIG.4). Hereinafter, node 1 that is the representative node during activeperiods AP2 to AP4 is described as “representative node 1.” Similarly,node 2 and node 3 as normal nodes without becoming the representativenode are described as “normal node 2” and “normal node 3.”

<Active Period AP2>

(7) Representative node 1 transmits a DGN advertisement message inadministrative slot=0 of active period AP2,

(8) normal node 2 transmits a data packet in data transmission slot=4 ofactive period AP2, and

(9) representative node 1 transmits an ACK in control slot=4 of activeperiod AP2. Since receiving, in control slot=4, the ACK for the datapacket transmitted in data transmission slot=4, normal node 2 stops datapacket transmission during the next active period AP3 (steps S50 to S54in FIG. 6).

(10) Normal node 3 receives this ACK (destined to node 2 though nodestination address) but it discards the ACK because it has transmittedno data packet in the same data transmission slot=4.

(11) Normal node 3 transmits a data packet in data transmission slot=7of active period AP2, and

(12) representative node 1 transmits an ACK in control slot=7 of activeperiod AP2. Since receiving, in control slot=7, the ACK for the datapacket transmitted in data transmission slot=7, normal node 3 stops datapacket transmission during the next active period AP3 (steps S50 to S54in FIG. 6).

(13) Normal node 2 receives this ACK (destined to node 3 through nodestination address) but it discards the ACK because it has transmittedno data packet in the same data transmission slot=7.

<Active Period AP3>

(14)(15) After completion of active period AP2, representative node 1judges in step S18 of FIG. 4 (judgment as to the presence of a datatransmission node) whether DM should be maintained. In this case, it isjudged that DM should be maintained because of the presence of a datatransmission node during active period AP2, and a DGN advertisementmessage is transmitted in administrative slot=0 of the next activeperiod AP3.

(16)(17) Since receiving the ACK during active period AP2 (Yes in stepS53 of FIG. 6), normal nodes 2, 3 stop data packet transmission duringthe next active period AP3 (step S54 in FIG. 6). Further, since the DGNadvertisement message was received in administrative slot=0 of activeperiod AP2 (Yes in step S57 of FIG. 6), DM is maintained.

<Active Period AP4>

(18)(19) After completion of active period AP3, representative node 1also judges in step S18 of FIG. 4 (judgment as to the presence of a datatransmission node) whether DM should be maintained. In this case, it isjudged that DM should not be maintained because no data transmissionnode is present during active period AP3, transmission of the DGNadvertisement message is stopped during active period AP4 (step S19),and a data packet is transmitted from its own node in data transmissionslot=2 of active period AP4.

(20)(21) Since normal nodes 2, 3 received the DGN advertisement messageduring active period AP3 (Yes in step S57 of FIG. 6), DM is maintained.

(22) The priority given to representative node 1 to become the CDGN atthe next opportunity to enter Dense Mode (DM) is reduced (step S25 inFIG. 4), and representative node 1 starts data packet transmission fromthe next active period.

(23)(24) Since normal nodes 2, 3 received no DGN advertisement messageduring active period AP4, termination of DM is judged, and they start(resume) data packet transmission from the next active period.

Second Embodiment of First Invention

FIG. 9 is a flowchart for explaining the operation of a candidate for arepresentative node (CDGN) according to a second embodiment of the firstinvention. In the second embodiment, the CDGN declaration message istransmitted in both the administrative slot (=0) and a control slot ofthe same active period. In FIG. 9, steps S101 to S104 are the same assteps S1 to S4, respectively, and their description will be omitted. Instep S104, after generation of the CDGN declaration message, a time slotfor transmitting a data packet is decided (step S105). Then, a controlslot for transmitting the CDGN declaration message is decided (stepS106), and the CDGN declaration message is transmitted in administrativeslot=0 (step S107).

It is then determined whether it is the timing of the time slot fortransmitting the data packet (step S108), and if so, processing proceedsto step S109. On the other hand, if not, processing proceeds to stepS111 to perform the reception processing shown in detail in FIG. 5, andprocessing proceeds to step S112. In step S109, a data packet istransmitted, data packet transmission is stopped (step S110), andprocessing proceeds to step S112. In step S112, it is determined whetherit is the timing of a control slot for transmitting the CDGN declarationmessage, and if so, the CDGN declaration message is transmitted (stepS113). Then, processing proceeds to step S115. In step S112, if it isnot the control slot for transmitting the CDGN declaration message, thereception processing shown in detail in FIG. 5 is performed, andprocessing proceeds to step S115. In step S115, it is determined whetherit is the final time slot. If so, processing returns to step S108, whileif not, processing proceeds to step S116.

In step S116, a DGN is decided from received (and transmitted) CDGNdeclaration messages, and if its own node becomes the DGN, a DGNadvertisement message is generated (step S117 to step S118), andprocessing proceeds to step S120. In step S117, if its own node does notbecome the DGN, it makes transition from the CDGN to a normal node inDense Mode (DM) (step S119), and processing ends. In step S120, the DGNadvertisement message is transmitted in time slot=0, and it is thendetermined whether any data packet has been received (step S121). Ifreceived, an ACK is transmitted in a control slot immediately followingthe data transmission slot in which the data packet was received (stepS122). It is then determined whether it is the final time slot (stepS123). If not, processing returns to step S121, while if not, processingproceeds to step S124.

It is determined in step S124 whether the number of time slots thatdetect collisions decreases to a number smaller than a reference value.If not decrease, processing returns to step S120 to continue DM, whiledecreases, processing proceeds to step S125. In step S125, transmissionof the DGN advertisement message is stopped during the next activeperiod, and in step S126, the priority of becoming the CDGN at the nextopportunity to enter DM is reduced. Then, this processing ends.

A second embodiment of the first invention will next be described withreference to FIG. 10. In FIG. 10, processing in steps S42-1 to S42-6 isdifferent from processing in steps S42 to S44 shown in FIG. 6. First, atime slot for transmitting a data packet is decided (step S41). It isthen determined whether CDGN declaration messages have been received ora collision has been detected in time slot=0 (step S42-1). If either ofthem is determined, processing proceeds to step S42-2, while if none ofthem is determined, processing branches to step S42-4. In step S42-2,data packet transmission is stopped, the reception processing shown indetail in FIG. 5 is performed (step S42-3), and processing proceeds tostep S45. In step S42-4, it is determined whether it is the time slotfor its own node to transmit a data packet. If so, the data packet istransmitted (step S42-5), and processing proceeds to step S45. On theother hand, if not, the reception processing shown in detail in FIG. 5is performed (step S42-6), and processing proceeds to step S45. Thepresence of the CDGN declaration messages means that nodes are congestedaround its own node including a node that has detected the occurrence ofa transmission collision. Therefore, the node judged to be Yes in stepS42-1 immediately stops data packet transmission (step S42-2) to avoidcausing the occurrence of a new transmission collision.

Processing in steps S45 to S47 is the same as that in FIG. 6, except foraddition of step S47 a between steps S47 and S48. In step S47, when aDGN is decided by a predetermined method from the received CDGNdeclaration messages, data packet transmission is resumed in step S47 a,and processing proceeds to step S48. Processing in step S48 andsubsequent steps is the same as that in FIG. 6, and its description willbe omitted.

FIG. 11 and FIG. 12 show an example operation of nodes 1, 2, and 3according to the second embodiment of the first invention. Similarly,due to limitations of space, FIG. 11 shows active periods AP1 and AP2,and FIG. 12 shows active periods AP3 and AP4.

<Active Period AP1>

(1) Node 1 that detected a collision during the previous active periodand decided transition to CDGN transmits a CDGN declaration message inthe administrative slot (=1) of active period AP1,

(2) node 2 that detected no collision during the previous active periodand decided transition to CDGN also transmits a CDGN declaration messagein the administrative slot (=1) of active period AP1, and

(3) node 3 that detected no collision during the previous active perioddetects a collision in the administrative slot (=0) of active periodAP1.

(4) Node 1 transmits a data packet in data transmission slot (=4) ofactive period AP1,

(5) node 1 transmits a CDGN declaration message in control slot (=4) ofactive period AP1,

(6) node 2 transmits a data packet in data transmission slot (=6) ofactive period AP1, and

(7) node 2 transmits a CDGN declaration message in control slot (=6) ofactive period AP1.

(8)(9) Nodes 1 and 2 select a DGN (representative node) by apredetermined method (for example, node having the smallest node ID)from received or transmitted CDGN declaration messages. Here, Node 1having the smallest node ID is selected as the DGN.

(10) Since detecting the collision in the administrative slot (=0) ofactive period AP1, node 3 stops packet transmission during active periodAP1 (steps S42-1 to S42-2 in FIG. 10). Further, from the CDGNdeclaration messages received in control slots (=4, 6), a DGN isselected by a predetermined method (for example, node having thesmallest node ID). Here, node 1 having the smallest node ID is selectedas the DGN. Here, node 2 that made transition to the CDGN makestransition to normal node (steps S116 to S119 in FIG. 9). Hereinafter,node 1 that is the representative node during active periods AP2 to AP4is described as “representative node 1.” Similarly, node 2 and node 3 asnormal nodes without becoming the representative node are described as“normal node 2” and “normal node 3.”

<Active Period AP2>

(11) Representative node 1 transmits a DGN advertisement message in theadministrative slot (=0) of active period AP2,

(12) normal node 2 transmits a data packet in the data transmission slot(=4) of active period AP2, and

(13) representative node 1 transmits an ACK in the control slot (=4) ofactive period AP2. Since receiving, in control slot=4, the ACK for thedata packet transmitted in data transmission slot=4, normal node 2 stopsdata packet transmission during the next active period AP3 (steps S50 toS54 in FIG. 10).

(14) Normal node 3 receives this ACK (destined to node 2 though nodestination address) but it discards the ACK because it has transmittedno data packet in the same data transmission slot=4.

(15) Normal node 3 transmits a data packet in data transmission slot(=7) of active period AP2, and

(16) representative node 1 transmits an ACK in control slot (=7) ofactive period AP2. Since receiving, in control slot=7, the ACK for thedata packet transmitted in data transmission slot=7, normal node 3 stopsdata packet transmission during the next active period AP3 (steps S50 toS54 in FIG. 10).

(17) Normal node 2 receives this ACK (destined to node 3 through nodestination address) but it discards the ACK because it has transmittedno data packet in the same data transmission slot=7.

(18) Representative node 1 judges, in steps S124 to S127 shown in FIG.9, whether DM should be maintained. For example, if the number ofcollision detecting slots decreases, it judges termination of DM, and itstops transmission of the DGN advertisement message during the nextactive period AP3. Further, it resumes data packet transmission duringthe next active period AP3.

(19)(20) Since receiving the ACK, normal nodes 2 and 3 stop data packettransmission during DM. However, they resume data packet transmissionwhen receiving of the DGN advertisement message ceases in theadministrative slot (=0).

<Active Period AP3>

(21) Normal node 2 transmits a data packet in data transmission slot(=1) of active period AP3,

(22) normal node 1 transmits a data packet in data transmission slot(=3) of active period AP3, and

(23) normal node 3 transmits a data packet in data transmission slot(=6) of active period AP3.

(24) Normal node 1 reduces its priority of becoming the CDGM at the nextopportunity to make transition to DM.

(25)(26) Since receiving no DGN advertisement message in administrativeslot(=0) of active period AP3, normal nodes 2 and 3 resume data packettransmission and transmit data packets at (21) and (23), respectively.

FIG. 13 shows the structure of a radio communication device (node) 10according to the first invention. Carriers on each time slot arereceived via a radio antenna 11, demodulated by radio receiving means12, and applied to collision detection means 13, CDGN declarationmessage analyzing means 14, DGN advertisement message analyzing means15, ACK analysis means 16, and data packet analyzing means 17. Acollision among carriers on each time slot is detected by the collisiondetection means 13, and a slot 19 a as a collision source is stored ininformation storage means 19. Further, a CDGN declaration message oneach time slot is analyzed by the CDGN declaration message analyzingmeans 14, and the analyzed CDGN declaration message 19 c is stored inthe information storage means 19. In the information storage means 19,the number of slots 19 b that have been used, a node ID 19 d of its ownnode decided as a DGN, and priority 19 e of making transition to a CDGNare also stored.

A DGN advertisement message, an ACK, and a data packet on each time slotare analyzed by the DGN advertisement message analyzing means 15, theACK analysis means 16, and the data packet analyzing means 17,respectively. Based on the analyzed DGN advertisement message and ACK,stop of data packet transmission is judged by “stop of data packettransmission controlling means” 18. “Transition to CDGN judging means”20 judges whether to make transition to the CDGN or reduces the“priority of making transition to the CDGN” 19 e based on the collisionsource slot 19 a and “the number of slots that have been used” 19 bstored in the information storage means 19. “Transition to DGN judgingmeans” 21 judges transition to the DGN based on the CDGN declarationmessage 19 c stored in the information storage means 19.

When the “transition to DGN judging means” 21 judges to make transitionto the DGN, “transmission of DGN advertisement message controllingmeans” 22 generates a DGN advertisement message, while when the“transition to DGN judging means” 20 judges to make transition to aCDGN, “transmission of CDGN declaration message controlling means” 23generates a CDGN declaration message. Further, when the “stop of datapacket transmission controlling means” 18 judges to stop data packettransmission, “data packet transmission controlling means” 24 stops datapacket transmission, and “ACK transmission controlling means” 25controls transmission of the ACK based on the data packet analyzed bythe data packet analyzing means 17. Messages and the like generated bythese transmission control means 22 to 25 are modulated by radiotransmission means 26, and transmitted via the radio antenna 11.

<Second Invention>

Next, embodiments of the second invention will be described. FIG. 15 isan explanatory diagram showing the structure of time slots in a radiocommunication method, a radio communication system, and a radiocommunication device according to the second invention. In the secondinvention, any period within a superframe of a constant cycle is definedas an active period AP and the rest is defined as a sleep (inactive)period iAP, and the active period AP is divided into plural time slots.When each of plural radio communication devices (nodes) uses each timeslot to perform time-division two-way communication, if each of theplural nodes detects a collision in each time slot, a collisionadvertisement message 201 is transmitted in a predetermined time slot(time slot=0 in FIG. 15) of the next active period AP, and the nextactive period AP is extended.

Further, a node that transmits a collision advertisement message 201adds not only its own data but also a packet 202 including the collisionadvertisement message 201 (0, i, ii, and iii in FIG. 15) to an emptytime slot (time slot=6 in FIG. 15) detected at random by CSMA during thenext active period AP. Then, when detection of collisions in theextended active period AP ceases, the extended active period AP isreturned to the original duration (reduction).

FIG. 16 is a diagram showing a format example of the collisionadvertisement message 201. The collision advertisement message 201consists of Type indicative of the kind of message (for example,Type=1), a collision slot indicative of a time slot that caused acollision, and the number of times of continuous transmission of thiscollision advertisement message 201 (Report No.), and the field of thenode ID of each transmission source. As an example, the field ofcollision slot is made up of the same number of bits as the number oftime slots, representing a bit map, where the position of a time slotthat caused a collision is bit=1 and the position of a time slot thatcaused no collision is bit=0. Thus, a node that has received thecollision advertisement message 201 can know whether a collision hasoccurred in a time slot in which it transmitted data last time.

First Embodiment of Second Invention

FIG. 17, FIG. 18, and FIG. 19 are flowcharts for explaining theoperation of nodes according to the first embodiment. In FIG. 17, it isfirst determined whether packet transmission is being stopped (stepS201). If being stopped, processing proceeds to step S202, while if notbeing stopped, processing branches to step S205. In step S202, packetreception processing shown in detail in FIG. 18 is performed, and it isthen determined whether the time slot timing is for the final slot (stepS203). If it is not the timing of the final time slot, processingreturns to step S201, while if it is the timing of the final time slot,processing proceeds to S204 to perform extension control processingshown in detail in FIG. 19, and processing returns to step S201. Sincethe extension control processing is performed by using all theprocessing results of collisions detected in each time slot andcollision advertisement messages 201 received in each time slot withinone active period AP (step S204), judgment in step S203 is made.

Next, the packet reception processing in step S202 will be describedwith reference to FIG. 18. It is first determined whether a collisionhas been detected (step S231). If detected, processing proceeds to stepS232, while if not detected, processing branches to step S235. In stepS232, a time slot that detected a collision is recorded, and it is thendetermined whether the time slot is the first time slot (=0) of thecurrent active period AP (step S233). Then, if it is time slot=0, thenext active period AP is extended to a certain length (step S234), andprocessing ends. On the other hand, if it is not time slot=0, processingends as is.

If no collision is detected in step S231, it is determined in step S235whether the time slot is time slot=0. If it is time slot=0, processingproceeds to step S236, while if it is not time slot=0, processingbranches to step S241. In step S236, it is determined whether thecollision advertisement message 201 has been received. If received,processing proceeds to step S237, while if not received, processing endsas is. In step S237, the next active period AP is extended to thecertain length, and it is then determined whether a collision of its ownnode that has occurred during the previous active period AP is describedin the received collision advertisement message 201 (in the field ofcollision slots in FIG. 15) (step S238). If the collision occurrence isdescribed, processing ends as is, while if not described, the number ofactive periods AP over which packet transmission is stopped is decided(step S239), packet transmission is stopped (step S240), and processingends.

If the time slot is not time slot=0 in step S235, the data part of thereceived packet is processed in step S241, and it is then determinedwhether packet 2 including the collision advertisement message 201 hasbeen received (step S242). If received, processing proceeds to stepS243, while if not received, processing ends as is. In step S243, thenext active period AP is extended to the certain length, and it is thendetermined whether a collision of its own node that has occurred duringthe previous active period AP is described in the received collisionadvertisement message 201 (in the field of collision slots in FIG. 15)(step S244). If the collision occurrence is described, processing endsas is, while if not described, the number of active periods AP overwhich packet transmission is stopped is decided (step S245), packettransmission is stopped (step S246), and processing ends.

Next, the extension control processing in step 204 will be described indetail with reference to FIG. 19. It is first judged by the packetreception processing (step 202) whether the next active period AP shouldbe extended (step S251 and S252). If should be extended, processingproceeds to step S253, while if should not be extended, processingbranches to step S255. In step S253, the collision advertisement message201 is generated, the next active period AP is extended to the certainlength (step S254), and processing ends. In step S255, the next activeperiod AP is effected by the normal length, and it is determined whetherthe collision advertisement message 201 is being currently transmitted(step S256). If the collision advertisement message 201 is beingtransmitted, transmission of the collision advertisement message 201 isstopped (step S257), Report No. of the collision advertisement message201 is set to 0 (step S258), and processing ends. If the collisionadvertisement message 201 is not being transmitted in step S256,processing ends as is.

Returning to FIG. 17, step S205 and subsequent steps will be described.If packet transmission is being stopped in step S201, it is determinedwhether the active period AP is currently extended (step S205). Ifextended, a time slot for transmitting a packet within the extendedactive period AP is decided (step S206), and processing proceeds to stepS208. On the other hand, if the active period AP is not currentlyextended in step S205, a time slot for transmitting a packet within theactive period AP that is not extended is decided (step S207), andprocessing proceeds to step S208.

In step S208, based on the processing in step S231 and S232 of FIG. 18,it is determined whether the collision advertisement message 201 shouldbe transmitted. If should be transmitted, processing proceeds to stepS209, while should not be transmitted, processing branches to step S218.In step S209, it is determined whether the timing of the time slot istime slot=0. If it is the timing of time slot=0, processing proceeds tostep S210, while if it is not the timing of time slot=0, processingbranches to step S12. In step S210, the collision advertisement message201 is transmitted, 1 is added to the number of times of continuoustransmission of the collision advertisement message (Report No.) (stepS211), and processing proceeds to step S221.

If it is not the timing of time slot=0 in step S209, it is determinedwhether it is the timing of a transmission time slot for its own node(step S212). If so, processing proceeds to step S213, while if not,processing branches to step S217. In step S213, it is determined whetherReport No.=1, and if so, the packet 202 including the collisionadvertisement message 201 and data is transmitted (step S214), 1 isadded to Report No. (step S215), and processing proceeds to step S221.If it is not Report No.=1 in step S213, a packet including data istransmitted (step S216), and processing proceeds to step S221. In stepS212, if it is not the timing of the transmission time slot for its ownnode, the packet reception processing shown in detail in FIG. 4 isperformed (step S217), and processing proceeds to step S221.

In step S208, if the collision advertisement message 201 should not betransmitted, it is determined whether it is the timing of thetransmission time slot for its own node (step S218). If so, a packetincluding data is transmitted (step S219), and processing proceeds tostep S221. On the other hand, if it is not the timing of thetransmission time slot for its own node, the packet reception processingshown in detail in FIG. 4 is performed (step S220), and processingproceeds to step S221. In step S221, it is determined whether it is thetiming of the final time slot. If not, processing returns to step S208,while if so, processing proceeds to step S222, the extension controlprocessing shown in detail in FIG. 19 is performed, and processingreturns to step S201.

FIG. 20 shows an operation example of the first embodiment of the secondinvention. Illustrated is a case where the first active period AP1 has anormal length (time slots=0, 1, . . . , 7), and collisions among packetstransmitted by peripheral nodes in time slots=1, 2, 3, 5 have beendetected. In this case, in the reception processing shown in FIG. 18,time slots=1, 2, 3, 5 that detected collisions are recorded, andextension of the next active period AP2 to the certain length (timeslots=0, 1, . . . , 15) is decided. Further, in the extension controlprocessing shown in FIG. 19, the collision advertisement message 1 isgenerated, and the next active period AP2 is extended to the certainlength (time slots=0, 1, . . . , 15).

During the next active period AP2, in the processing of steps S208 toS211 shown in FIG. 17, the collision advertisement message 1 istransmitted in time slot=0, and the packet 202 including the collisionadvertisement message 201 and data is transmitted in time slot=6. Then,when a collision has been detected during the next active period AP2,the collision advertisement message 201 is transmitted in time slot=0 ofthe next active period AP3 (time slots=0, 1, . . . , 15). Further, whenno collision has been detected during this active period AP3, the nextactive period AP4 is returned to the original length (time slots=0, 1, .. . , 7), and transmission of the collision advertisement message 201 isstopped in time slot=0.

Second Embodiment of Second Invention

In the first embodiment of the second invention, the next active periodAP is extended when a collision has been detected. On the contrary, inthe second embodiment of the second invention, the current active periodAP is extended when a collision has been detected. The second embodimentof the second invention will be described with reference to FIGS. 21 to24. In this embodiment, although the number of time slots within anormal active period AP and the number of time slots within an extendedactive period AP are expressed in specific figures as (time slots=0, 1,. . . , 7) and (time slots=0, 1, . . . , 15), respectively, thisinvention is not limited thereto. In FIG. 21, S205 a is added betweenstep S205 and step S206 shown in FIG. 17, step S209 a is added betweenS209 and steps S210, S212, and processing in step S221 a is differentfrom step S221 shown in FIG. 17. As a result of judgment in step S205 asto whether the active period AP is currently extended, if beingextended, processing proceeds to step S205 a, and it is determinedwhether the transmission time slot is undecided. If undecided,processing proceeds to step S206, a time slot for transmitting a packetwithin the extended active period AP is decided, and processing proceedsstep S208. On the other hand, if the transmission time slot is notundecided in step S205 a, processing proceeds to step S208 as is.

Further, in step S209, it is determined whether the timing of the timeslot is time slot=0. If it is not the timing of time slot=0, processingproceeds to step S209 a to determine whether it is time slot=7 and thenumber of times of continuous transmission of the collisionadvertisement message (Report No.) is 0. If so, processing proceeds tostep S210 to transmit the collision advertisement message 201, while ifnot, processing branches to step S212. Further, in processing step S221a, it is determined whether it is the final time slot (=6 or 15). Ifnot, processing returns to step S208, while if so, processing proceedsto step S222. The other processing steps are the same as those in FIG.17, and their description will be omitted. The reason why time slot=6 iscited in step S221 as the time slot judged to be the final time slot isthat the first time slot 0 and the last time slot 7 in the normal activeperiod length (time slots=0, 1, . . . , 7) are set as predetermined timeslots used for transmission of the collision advertisement message.

In packet reception processing shown in FIG. 22, processing steps S234a, S237 a, and S243 a are different from steps S234, S237, and S243shown in FIG. 18, respectively, in that the current active period AP isextended to the certain length (time slots=0 to 15). The otherprocessing steps are the same as those in FIG. 18, and their descriptionwill be omitted. Further, in extension control processing shown in FIG.23, processing step S254 a is different from step S254 shown in FIG. 19,and steps S259, S260 are added after step S254 a. In step S254 a, thecurrent active period AP is extended to the certain length (time slots=0to 15), and it is then determined whether it is time slot=7 (step S259).If it is time slot=7, a packet transmission slot is decided within theextended part of the active period AP (step S260), and processing ends.On the other hand, if it is not time slot=7, processing ends as is. Theother processing steps are the same as those in FIG. 19, and theirdescription will be omitted.

FIG. 24 shows a case, where collisions among packets transmitted byperipheral nodes in time slots=1, 2, 3, 5 have been detected in thefirst length (time slots=0, 1, . . . , 7) of the first active periodAP1, as an operation example of the second embodiment of the secondinvention. In this case, in the reception processing shown in FIG. 22,time slots=1, 2, 3, 5 that detected collisions in step S232 arerecorded, and the current active period AP1 is extended in step S234 ato the certain length (time slots=0, 1, . . . , 15). Then, the collisionadvertisement message 1 is transmitted in time slot=7 of the currentextended active period AP1, and the packet 2 including the collisionadvertisement message 1 and data is transmitted in time slot=13. Then,if a collision has been detected during this active period AP1, thecollision advertisement message 201 is transmitted in time slot=0 of thenext active period AP2 (time slots=0, 1, . . . , 15), while if nocollision has been detected during this active period AP2, the nextactive period AP3 is returned to the original length, and transmissionof the collision advertisement message 1 is stopped in time slot=0.

FIG. 25 shows the structure of a radio communication device (node) 210according to the second invention. Carriers on each time slot arereceived via a radio antenna 211, demodulated by radio reception means212, and applied to collision detection means 213, receiving slotanalyzing means 215, and collision advertisement message analyzing means216. A collision among carriers on each time slot is detected by thecollision detection means 213, and the detected slot 218 a as acollision source is stored in information storage means 218. Further, areceiving slot on each time slot is analyzed by the receiving slotanalyzing means 215, and the collision advertisement message 201 isanalyzed by the collision advertisement message analyzing means 216.Based on the collision source slot 218 a detected by the collisiondetection means 213, the receiving slot analyzed by the receiving slotanalyzing means 215, and the collision advertisement message 201analyzed by the collision advertisement message analyzing means 216,“extension of active period controlling means” 214 determines whetherthe active period should be extended, the length of the active period isdecided, and the decided length 218 c of this active period is stored inthe information storage means 218. Further, based on the collisionadvertisement message 201 analyzed by the collision advertisementmessage analyzing means 216, “stop of packet transmission controllingmeans 217 decides a packet transmission stopping period 218 b, and thisdecided packet transmission stopping period 218 b is stored in theinformation storage means 218.

Based on the collision source slot 218 a stored in the informationstorage means 218, the packet transmission stopping period 218 b, andthe active period length 218 c, “data transmission slot deciding means”219 decides a time slot for data transmission, and collisionadvertisement message generating means 221 generates the collisionadvertisement message 201. Transmission timing is so controlled that thegenerated collision advertisement message 201 is transmitted in theabove-mentioned transmission time slots=0, 7 for the collisionadvertisement message 201 by means of “transmission of collisionadvertisement message controlling means” 222. Further, “packet includingdata generating means” 220 generates a “packet including data” in thetime slot decided by the “data transmission slot deciding means” 219,and “the collision advertisement message 201 and the packet 202.” This“packet including data” and “the collision advertisement message 201 andthe packet 202 including data” are modulated by radio transmission means223 and transmitted via the radio antenna 211.

<Third Invention>

Next, an embodiment of the third invention will be described. FIG. 26shows radio node classification and the structure of a system in thisembodiment. This system is connected to an external wired/wirelessnetwork 301 (for example, the Internet), and consists of a gateway (GW)302 communicable with the external network 301 and capable of supplyingpower such as commercial power supply, and small battery-operated RFtags 303 a, 303 b as radio communication nodes 303. The RF tags 303 a,303 b, which can send and receive, comes ready to support two-way dataexchange, and are called P2P (Point to Point) tags below. The P2P tags303 a, 303 b are of two types, namely a P2P-S tag 303 a as a(Stationary) P2P tag designed not to anticipate movement afterinstallation and a P2P-M tag 303 b as a (Mobile) P2P designed to involvemovement such as to be carried by a person.

As shown in FIG. 26, each of the P2P tag 303 a, 303 b exchanges its IDin an adhoc manner with any of the P2P tags 303 a, 303 b located in itscommunicable range. Thus, the moving P2P-M tag 303 b enables the P2Ptags 303 a, 303 b to exchange and accumulate IDs on a reciprocal basis,and hence to keep historical records of one another's contact. Thismakes it possible to accumulate activity history of a certain person inthe P2P-M tag 303 b and a history of people who pass a certain point inthe P2P-S tag 303 a. For example, as a specific application example, acase is considered where a history of behavior of people and their wayof contact with one another is acquired. In this case, GW2 is positionedin a place where commercial power supply is available, and a largenumber of P2P-S tags 303 a are positioned in other places, so that ahistory of behavior of people who carry the P2P-M tags 303 b and theirway of contact can be acquired.

Further, in such an application that people just send and receive theirIDs to keep a history of contact using their radio communication nodes303, since there is no need for senders of information to identifyreceivers, each of the tags 303 a, 303 b has only to broadcast its IDand each of the tag 303 a, 303 b that has received it has only toaccumulate it.

FIG. 27 shows the structure of a superframe period T_p in thisembodiment. According to the third invention, as shown in FIG. 27( a),the superframe period T_p has an active period Tact during which thetags 303 a, 303 b as the radio communication nodes 303 exchange frames,and a sleep period (=T_p-Tact) during which radio blocks (to bedescribed later in FIG. 29) of the tags 303 a, 303 b stop operating. Theactive period Tact consists of a variable number of time slots TS asshown in FIG. 27( b) (the number of time slots=16 in the drawing). Eachmoving tag 303 b selects each time slot TS within the active period Tactperiodically at random, and transmits its own information in a frame tothe selected time slot TS.

Each node 303 has the active period Tact for frame transmission andreception, and the sleep period (=T_p-Tact) during which the radio blockstops operating, thereby achieving first power saving. The active periodTact consists of a variable number of time slots, and each moving node303 attempts periodic transmission of its own information by CSMA(Carrier Sense Multiple Access) to time slots within the active periodTact in order from the first time slot. Therefore, the time slots areused in order from the first one.

FIG. 28 shows a sequence of response confirmation (ACK) according tothis invention. Indicated in FIG. 28 is such a state that three nodes,namely node A, node B, and node C, are broadcasting their frames F[A],F[B], and F[C], respectively. In the third invention, each node A-Cexchanges and accumulates information when they pass each other, andtransmits the accumulated information only to a specific node (GW2 inFIG. 26). Thus, since a frame received from a certain node is nevertransferred to another node, the broadcast frames F[A], F[B], and F[C]are sent and received only among the nodes A-C located in theircommunication range.

FIG. 28 shows such a state that each node A-C is transmitting its owninformation in frame F[A], F[B], or F[C] to a time slot TS selected atrandom in superframe period N−1. Note that node A and node C are locatedin places where they cannot directly communicate with each other in thisexample. It is assumed that frame F[A] transmitted by node A issuccessfully received by node B, frame F[B] transmitted by node B issuccessfully received by node A and node C, and frame F[C] transmittedby node C is successfully received by node B.

When nodes A, B, and C transmit their frames F[A:b], F[B:a,c], andF[C:b] during the next superframe period N, respectively, they transmitthe frames by adding information on nodes received in the respectiveframes F[A:b], F[B:a,c], and F[C:b] during the previous superframeperiod N−1. This enables each node A, B, C to recognize, from ACKinformation attached in a frame of another node and coming together,that its own frame F[A], F[B], F[C] transmitted during the previoussuperframe period N−1 has been received. In addition, node B can alsoconfirm reception at plural nodes A, C by receiving ACK information fromnode A and node C.

Use of such ACK information makes it possible not only to confirm thatits own frame has been actually received, but also to indirectlyunderstand how many nodes another node communicate with. This allows amoving node to know how many communicable nodes are in the vicinity of acorrespondence node communicating with the moving node at present. Thethird invention uses such ACK information to set the number of timeslots used for the next superframe period from the number of time slotsreceived by itself during the superframe period and the number of nodesexpected from the received frames.

The structure of a node 303 of the third invention will next bedescribed with reference to FIG. 29. The node 303 of this inventionconsists of a radio block 311 having a transmitter section 311 a and areceiver section 311 b, a control section 312, an ID storage section313, a clock 314, and a power supply section 315. The transmittersection 311 a has the function of transmitting frame F including its IDby radio. In the node 303 of the third invention, the transmittersection 311 a transmits frames by broadcasting its ID periodically. Thereceiver section 311 b has the function of receiving frames includingIDs transmitted by other nodes 303 in the same way.

The control section 312 has the function of controlling the operation ofthis node 303. The details of the function of the control section 312will be described later with reference to FIG. 30. The ID accumulationsection 313 has the function of accumulating IDs of other nodes 303received at the receiver section 311 b. When an ID is accumulated in theID accumulation section 313, time information on that time may berecorded together with the ID. Its own ID information is also recorded.The clock 314 has the function of outputting clock signals for graspingtimings for frame transmission in the transmitter section 311 a andframe reception in the receiver section 311 b. The power supply section315 is a power supply built in the node 303 to make the node 303communicable even if it moves to any place. For example, the powersupply is a battery mounted in the case of the node 303.

Referring next to FIG. 30, the function of the control section 312 inthe embodiment of this invention will be described. Specifically, thecontrol section 312 consists of a time slot adjusting section 321, aframe analysis section 322, a frame generation section 323, an ACKgeneration section 324, and a number of slots controlling section 325.The time slot adjusting section 321 has not only the function ofperforming control of time slot synchronization including superframeperiod synchronization, but also the function of receiving frame F andtransmitting, using CSMA, frame F generated for a possible time slot TS.The frame analysis section 322 has not only the function of analyzingthe reception status in each time slot TS and notifying it to the ACKgeneration section 324 and the number of slots controlling section 325,but also the function of acquiring ID information from the receivedframe F and notifying it to the ID accumulation section 313.

The ACK generation section 324 generates, based on information from theframe analysis section 322, an ACK field to be added to frame F to betransmitted by itself next time. The number of slots controlling section325 decides, based on the information from the frame analysis section322, the number of time slots to be set in its own node for the nextsuperframe period. Specifically, processing illustrated in a flowchartto be described later is performed. The frame generation section 323generates frame F from its own ID, time slot information to betransmitted, and ACK field information notified from the ACK generationsection 324.

FIG. 31 shows the structure of frame F exchanged among respective tags(nodes 303). Each node 303 generates frame F with a fixed lengthtransmittable in one time slot TS. Specifically, frame F consists offields each for the slot number of each time slot TS transmitted byitself, the type of node 303, its own ID number (ID), and an ACK fieldfor notifying the reception status to the sender node in response toreception of frame F from another node. The third invention featuresthat receipt response information on the frame received from anothernode 303 in another time slot TS is included in frame F for transmittingits own information. Specifically, the ACK field consists of fieldsindicative of respective time slots TS1-TS16 of a superframe SFspecified in the system, and the reception status in each time slotTS1-TS16 is stored as ACK information.

Unlike a method, so-called passive ACK, for responding individuallyusing a receiver node ID or transmitting a frame of the receiver node tonotify reception, the third invention uses an ACK field with a fixedlength for a given number of time slots to provide its own receptioninformation at a time to all nodes as transmission sources receivedduring the previous superframe period N−1. Therefore, 16×16 receptionstates are provided in one superframe period T_p. Further, each piece ofinformation for each time slot in the ACK field contains two bits, andthe status is indicated as follows.

00: no reception

10: reception with error

11: successful reception

“10: reception with error” includes a case where received frame F hasbeen discarded due to a bit error or frame error, and a case where frameF was not able to be received correctly due to a collision. Thus, thereception status of fixed time slots is notified instead of using an ACKfor each individual node, and this makes it possible to keep the framelength fixed for the number of ACKs, compared to the case of confirmingresponses to plural nodes using individual ID nodes. Further,notification can be made with very small amounts of information.

Further, in addition to the TS fields TS1-TS16 corresponding to therespective time slots, a special one-bit flag field (SP field) is addedto this ACK field. Though the details will be described later, thisfield is set to ON (bit=1) when its own frame was not able to betransmitted in the set number of time slots.

Referring next to FIG. 32, a method of generating the ACK field in theACK generation section 324 will be described. Based on the informationfrom the frame analysis section 322, the ACK generation section 324configures the settings on the above-mentioned two-bit TS fieldsTS1-TS16 for the respective time slots TS received during a superframeperiod (step S301). Thus, time slots TS transmitted and received are alldescribed in corresponding TS fields TS1-TS16 including errors due tocollisions or the like.

Further, when there was no opportunity for itself to transmit inrespective slots until the end of a set superframe period because ofCSMA and hence transmission was not able to be performed (No in stepS302), the SP field is set to ON to indicate it (step S303). Thiscorresponds to such a case that the node moves to an environment whereit communicates with more nodes 303 and has no opportunity for itself totransmit because the number of nodes exceeds the number of time slots Nset in the superframe period. In such a case, the node will inform othernodes of the shortage of time slots as well as the TS fields in the ACKfield inserted in its own frame to indicate transmission and receptionwere performed by itself. For example, if there are a large number offrames F with their SP fields set to ON during reception, it means thatsuch a number of nodes 303 had no communication opportunity and hencewas not able to perform transmission.

Next, the operation of the number of slots controlling section 325 willbe described. When a node has shifted or moved from an environmentcapable of communicating with a large number of nodes 303 to anenvironment where there are fewer nodes 303 around it, it is importantto reduce the number of time slots N used for reception during asuperframe period from the viewpoint of power saving. On the contrary,when the node has shifted or moved from an environment for communicationwith few nodes 303 to an environment where a large number of nodes 303exist, it is important to increase the number of time slots N to anappropriate number in order to exchange data with more nodes 303. Thus,the number of slots controlling section 325 serves to autonomously setthe number of time slots N in the superframe period in such a manner.

FIG. 33 is a flowchart showing processing in the number of slotscontrolling section 325. Based on the information from the ACKgeneration section 324, reception information on its own node 303 duringa superframe period concerned is grasped to check the time slotconditions in the superframe period. Then, candidates for the number oftime slots N of the next superframe period are determined from thisinformation. They are added up in such a manner that 1 is added to eachof frames that were its own transmission and successful reception (=11),and 2 is added to states of error reception (=10) due to collisions orthe like. The reason why 2 is added to the states of error reception(=10) is to take into account the presence of plural nodes that could besubjected to collisions. However, if there is no frame received, i.e.,when the ACK generation section 324 has only the frame informationtransmitted by itself, the number of time slots N for the nextsuperframe period is set to two slots in case of reception from anothernode to its transmission time slot.

When frame reception was performed, the number of time slots is added upin the same manner from the ACK field in the frame F that was successfulreception(=11) based on the information from the frame analysis section322 to determine candidates for the number of time slots N of the nextsuperframe period. Among the candidates for the number of time slotsthus determined, the maximum value is set as the number of basic timeslots N during the next superframe period (step S311).

Next, the number of frames A set by the SP field in the ACK field of asuccessfully received frame is added to the number of basic time slots N(step S312). Therefore, the number of time slots N for the nextsuperframe period is N+A. Thus, the number of frames A set by the SPfield is added to the number of basic time slots N to set the number oftime slots N=N+A for the next superframe period, and this increases thenumber of time slots N by the number of nodes 303, A, which were not beable to transmit. The status of the SP field in the ACK field generatedby its own node 303 is also included therein (steps S313 and S314).Thus, the node 303 that has shifted to the environment where there are alarge number of nodes 303 has other nodes 303 increase the number oftime slots N by the number of nodes 303 that were not able to transmit,increasing the possibility of being received.

Thus, the number of time slots N is increased or decreased based notonly on its own reception status, but also on the ACK information fromother nodes. This makes it possible to achieve power saving while usingtime slots efficiently. Further, the SP field is provided in the ACKfield to grasp the number of nodes that were not able to transmit duringthe previous superframe period. This makes it possible to grasp theshortage of time slots and to increase the number of time slots in onego.

<Fourth Invention>

Since the classification of radio communication devices (nodes) and thestructure of a system in an embodiment of the fourth invention are thesame as those in FIG. 26 according to the third invention, theirdescription will be omitted. Further, since the structure of thesuperframe period T_p in the embodiment of the fourth invention is alsothe same as that in FIG. 27 according to the third invention, itsdescription will also be omitted. In addition, since the sequence ofresponse confirmation (ACK) in the embodiment of the fourth invention isalso the same as that in FIG. 28 according to the third invention, itsdescription will be omitted as well.

FIG. 34 shows the structure of frame F exchanged among respective tags(nodes 303). Each node 303 generates frame F with a fixed lengthtransmittable in one time slot TS. Specifically, frame F consists offields each for the slot number of each time slot TS transmitted byitself, the type of node 303, its own ID number (ID), and an ACK fieldfor notifying the reception status to the sender node in response toreception of frame F from another node. The fourth invention featuresthat receipt response information on the frame received from anothernode 303 in another time slot TS is included in frame F for transmittingits own information. Specifically, the ACK field consists of fieldsindicative of respective time slots TS1-TS16 of a superframe SFspecified in the system, and the reception status in each time slotTS1-TS16 is stored as ACK information.

Unlike a method, so-called passive ACK, for responding individuallyusing a sender node ID or transmitting a frame of the sender node tonotify reception, the fourth invention also uses the ACK field with afixed length for a given number of time slots to provide its ownreception information at a time to all nodes as transmission sourcesreceived during the previous superframe period N−1. Therefore, 16×16reception states are provided in one superframe period T_p. Further,each piece of information for each time slot in the ACK field containstwo bits, and the status is indicated as follows.

00: no reception

10: reception with error

11: successful reception

“10: reception with error” includes a case where received frame F hasbeen discarded due to a bit error or frame error, and a case where frameF was not able to be received correctly due to a collision. Thus, thereception status of fixed time slots is notified instead of using an ACKspecifying each individual node, and this makes it possible to keep theframe length fixed for the number of ACKs, compared to the case ofconfirming responses to plural nodes using individual ID nodes. Further,notification can be made with very small amounts of information.

Referring next to FIG. 35, a method of generating the ACK field will bedescribed. FIG. 35 illustrates the method of generating the ACK fieldusing two timings of superframe periods N−1 and N for a certain node303, assuming a case where the node 303 transmits frame F in “timeslot:3” during the N-th superframe period. In the ACK field of frame Ftransmitted by the node 303 at this time, states of all time slotsreceived by itself during the previous superframe period N−1 aredescribed per time slot. For example, they are expressed as follow:

-   -   frame received successfully in “time slot:1” (hereinafter        referred to as TS1) (=11),    -   frame received as well in TS2 (=11),    -   no frame reception in TS3 (=00),    -   . . .    -   frame received in TS6 but could not be completed correctly        (=10), . . . .        Thus, the reception state of each time slot during the previous        superframe period N−1 is always notified to the node 303 during        the superframe period N.

FIG. 36 shows a confirmation method using the ACK field upon superframereception. After completion of reception during one superframe period N(all time slots TS=all frames), the reception status of time slots ofeach node 303 during the previous superframe period N−1 can be graspedfrom frame F received successfully. Each node 303 holds the slot numberused by itself to broadcast during the previous superframe period N−1 tocheck a corresponding TS portion (TS7 in FIG. 36) of the ACK field, andthis makes it possible to know the reception status of the previousframe F transmitted by itself and received by other nodes 303.Considering that the node 303 moves, reception information on frame Ftransmitted by another node 303 could be included. However, the ID ofthe node 303 that transmitted the information can be checked at the sametime. In such a case, for example, if it is information from a new nodeother than the node received by itself during the previous superframeperiod N−1, it can be considered that the node concerned leaves the ACKinformation out.

The outline of the structure of the node 303 of the fourth inventionshown in FIG. 37 is the same as that of the third invention in FIG. 29,except for the control section 312. The function of a control section312 a of the fourth invention will be described with reference to FIG.37. The ID accumulation section 313 has the function of accumulating IDsof other nodes 303 received at the receiver section 311 b. When an ID isaccumulated in the ID accumulation section 313, time information on thattime may be recorded together with the ID. Its own ID information isalso recorded. The clock 314 has the function of outputting clocksignals for grasping timings for frame transmission in the transmittersection 311 a and frame reception in the receiver section 311 b. Thepower supply section 315 is a power supply built in the node 303 to makethe node 303 movable to any place. For example, the power supply is abattery mounted in the case of the node 303.

Referring next to FIG. 38, the function of a control section 312 a inthe embodiment of the fourth invention will be described. Specifically,the control section 312 a consists of the time slot adjusting section321, the frame analysis section 322, the frame generation section 323,the ACK generation section 324, and a congestion control section 325 a.The time slot adjusting section 321 has not only the function ofperforming control of time slot synchronization including superframeperiod synchronization, but also the function of receiving frame F andtransmitting frame F to a time slot TS selected at random. The frameanalysis section 322 has not only the function of analyzing thereception status in each time slot TS and notifying it to the ACKgeneration section 324 and the congestion control section 325 a, butalso the function of acquiring ID information from the received frame Fand notifying it to the ID accumulation section 313.

The ACK generation section 324 generates, based on information from theframe analysis section 322, an ACK field to be added to frame F to betransmitted by itself next time. The congestion control section 325 amakes a judgment on congestion based on information from the frameanalysis section 322 to make the frame generation section 323 and thetime slot adjusting section 321 effectuate the result of determinationto stop frame transmission or resume frame transmission. To be specific,processing illustrated in a flowchart to be described later isperformed. The frame generation section 323 generates frame F from itsown ID, time slot information to be transmitted, and ACK fieldinformation notified from the ACK generation section 324.

Next, an operation at the time of congestion will be described. When alarge number of nodes 303 are congested within a radio communicationrange, such as when a person holding a node 303 is waiting for a signalat a traffic intersection, the number of time slots in a superframeperiod could become smaller than the number of node communicable in thecommunication range. In such a case, even if access control by CSMA(Carrier Sense Multiple Access) is performed, some nodes 303 may not beable to receive frames due to a collision, or some nodes 303 can havetransmission opportunities continuously but the others may not be ableto have the transmission opportunity repeatedly depending on the timingto make them unable to transmit frames. In this invention, the number ofnodes 303 to transmit frame F during occurrence of congestion is reducedto avoid the congestion. This requires each node 303 to control thetiming of stopping transmission of frame F and the timing of resumingtransmission during congestion.

FIG. 39 to FIG. 41 are flowcharts showing processing in the congestioncontrol section 325 a. First, as shown in FIG. 39, if it is operating ina reduced time slot mode during congestion as a result of theinformation from the frame analysis section 322 (Yes in step S401), thecongestion control section 325 a performs return-to-transmissiondetermination processing (step S402), while if it is operating in anormal time slot mode (No in step S401), the congestion control section325 a performs stop-of-transmission determination processing (stepS403).

Referring to FIG. 40, the stop-of-transmission determination processing(step S403) will be described in detail. Upon completion of reception inone superframe n, it is determined whether the number of time slots thatits own node 303 performed successful reception (=11) and errorreception (=10) during the superframe n exceeds a congestion thresholdvalue A (step S411). If it does not exceed the congestion thresholdvalue A (No in step S411), it is determined not to be in a congestionstate yet, and a normal operation is performed.

If it exceeds the congestion threshold value A (Yes in step S411), theACK field of frame F that was successful reception (=11) is checked todetermine whether the number of slots used by its own node and othernodes indicated by the ACK field exceeds a congestion threshold value B(step S412). If it does not exceed the congestion threshold value B (Noin step S412), congestion is not determined yet because it may be a setof nodes 303 temporarily gathering when they pass each other, and normalframe transmission is performed.

If it exceeds the congestion threshold value B (Yes in step S412), thenumber of successful receptions (=11) for time slots in which itselftransmitted during the previous superframe period is checked in the samemanner from the ACK fields of all frames that were successful reception(=11) (step S413). If the number of receptions equal to or more than athreshold value C is confirmed (Yes in step S413), frame transmissionduring the next superframe is stopped (step S414), and the mode ischanged to a reduced time slot operation mode in which the time slotsthat construct a superframe are reduced (step S415). If the number ofreceptions equal to or more than a threshold value C is not confirmed(No in step S413), normal frame transmission is performed to exchangeits information though it is in a congestion state.

The reduced time slot operation mode is to reduce the number of timeslots for reception in order to reduce power consumption when the nodeitself stops transmission during congestion until the congestion isavoided. The congestion state means that nodes have many correspondencepartners to exchange information with each other, i.e., it means thatthe number of nodes that exchange and accumulate information on acertain node 303 increases. Further, in such a situation that nodes 303densely gather together, it is conceivable that there is relatively lessmovement of nodes 303, and hence that transmission and reception betweenthe same pair of nodes 303 increase if the congestion state persists.Therefore, the reduction of information to be received by andaccumulated in a node 303, which has stopped its frame transmission inthe congestion state, until elimination of the congestion state iseffective means for radio nodes to which power saving is an importantchallenge.

Referring next to FIG. 41, the return-to-transmission determinationprocessing when it is operating in the reduced time slot operation modeafter transmission is stopped (step S402) will be described in detail.In the reduced time slot mode, the ACK field of frame F first receivedis used to determine a congestion state of the surroundings. If thenumber of slots used, which is indicated by the ACK field of frame Fthat was the first successful reception (=11), is equal to or less thana congestion threshold value D (Yes in step S421), it is determined thatthe congestion state has been avoided. Therefore, transmission of itsframe F is resumed from the next superframe period (step S422), and themode is changed to the normal time slot operation mode (step S423). Ifit is not equal to or less than the congestion threshold value D (No instep S421), it is determined to remain in the congestion state.Therefore, the mode enters a sleep mode without using subsequent timeslots, and the same processing is repeated in the next superframe.

FIG. 42 shows an example of the reception status of each time slot. InFIG. 42( a), as described with reference to FIG. 36, each of the nodes303 first transmits frame F including the ACK field as responseinformation (no reception: 00, successful reception: 11, errorreception: 10) to frames received from other nodes 303. FIG. 42( b)shows that the number of time slots used (successful reception: 11,error reception: 10) is high. When each node determines this and stopstransmission, the number of time slots used (successful reception: 11,error reception: 10) is reduced, allowing each node 303 to determinethis and resume transmission.

Since the elimination of congestion is thus determined, the state ofcongestion can be determined in a shorter operating time by usinginformation of the ACK field included in certain reception frame F,rather than by receiving all times slots to check the number of timeslots used, thereby making it possible to achieve power saving duringcongestion.

Note that each of the functional blocks used in describing theaforementioned embodiments is implemented as an LSI (Large ScaleIntegration) typified by an integrated circuit. Each of them may be madeup of one chip individually, or they may be made up of one chip toinclude some or all of them. Here, although the LSI is assumed, it maybe called an IC (Integrated Circuit), a system LSI, a super LSI, or anultra LSI depending on the degree of integration. Further, the techniquefor creation of an integrated circuit is not limited to LSI, and it maybe implemented by a private circuit or a general-purpose processor. AnFPGA (Field Programmable Gate Array) capable of programming after LSImanufacturing or a reconfigurable processor capable of reconfiguringconnections or settings of circuit cells within the LSI may also beemployed. In addition, if integrated circuit technology capable ofreplacing LSI emerges with development of semiconductor technology oranother technology derived therefrom, the technology may be used tointegrate the functional blocks. For example, applications ofbiotechnology may be possible.

INDUSTRIAL APPLICABILITY

The first invention has the effect of making it possible to prevent acollision in such a state that radio communication devices arecongested, and is applicable to other network devices as well as thesmall battery-powered node for the radio communication network,especially for the electronic tag system in which small data isexchanged.

The second invention has the effects of making it possible toautonomously increase the opportunity of transmission when a collisionoccurs in such a state that radio communication devices are congested,and making it possible to increase the number of nodes that stoptransmission in order to reduce the number of nodes that attempttransmission at a time. The second invention is applicable to othernetwork devices as well as the small battery-powered node for the radiocommunication network, especially for the electronic tag system in whichsmall data is exchanged.

The third invention has the effect of making it possible to operate withan appropriate number of time slots in radio communication foradvertising its own information to an unspecified number of radiocommunication devices that involve movement, and hence to achieve powersaving. The third invention is applicable to other network devices aswell as the small battery-powered node for the radio communicationnetwork, especially for the electronic tag system in which small data isexchanged.

The fourth invention has the effect of making it possible toautonomously stop transmission using response confirmation in radiocommunication for advertising its own information to an unspecifiednumber of radio communication devices that involve movement withoutincreasing congestion during congestion, and to autonomously determinethe elimination of a congestion state so as to resume transmission. Thefourth invention is applicable to other network devices as well as thesmall battery-powered node for the radio communication network,especially for the electronic tag system in which small data isexchanged.

1. A radio communication method, in which any period within a superframeof a constant cycle is defined as an active period and rest is definedas a sleep period, and the active period is divided into plural timeslots to enable each of plural radio communication devices to performtime-division two-way communication using each time slot, the methodcomprising: a step of allowing each of the plural radio communicationdevices to detect, based on a communication condition in each time slot,such a state that plural radio communication devices are congested, andto decide one of the plural radio communication devices as arepresentative node; a step of allowing a first radio communicationdevice decided as the representative node to transmit a representativenode advertisement message advertising that the first radiocommunication device becomes the representative node; a step of allowinga second radio communication device, which has not been decided as therepresentative node, to transmit a data packet when receiving therepresentative node advertisement message; a step of allowing the firstradio communication device to transmit a confirmation message whenreceiving the data packet after transmitting the representative nodeadvertisement message; and a step of allowing the second radiocommunication device to stop data packet transmission during animmediately following active period when receiving the confirmationmessage after transmitting the data packet.
 2. The radio communicationmethod according to claim 1 further comprising: a step of allowing thefirst radio communication device to stop transmission of therepresentative node advertisement message during the immediatelyfollowing active period when not receiving the data packet aftertransmitting the confirmation message or when the number of collisiondetecting time slots is equal to or less than a reference value; and astep of allowing the second radio communication device to resume datapacket transmission during the immediately following active period whennot receiving the representative node advertisement message afterstopping the data packet transmission.
 3. The radio communication methodaccording to claim 1, wherein when the representative node is decided,each of the plural radio communication device detects, based on thecommunication condition in each time slot, such a state that pluralradio communication devices are congested, and transmits, during theimmediately following active period, a representative node candidatedeclaration message declaring that the radio communication devicebecomes a representative node candidate, and each of plural radiocommunication devices that have received and transmitted therepresentative node candidate declaration message decides, based on apredetermined method, one of the plural radio communication devices asthe representative node.
 4. The radio communication method according toclaim 3, wherein when the first radio communication device decided asthe representative node stops transmission of the representative nodeadvertisement message, priority of becoming a representative nodecandidate next time is reduced.
 5. A radio communication system, inwhich any period within a superframe of a constant cycle is defined asan active period and rest is defined as a sleep period, and the activeperiod is divided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising: means for allowing each ofthe plural radio communication devices to detect, based on acommunication condition in each time slot, such a state that pluralradio communication devices are congested, and to decide one of theplural radio communication devices as a representative node; means forallowing a first radio communication device decided as therepresentative node to transmit a representative node advertisementmessage advertising that the first radio communication device becomesthe representative node; means for allowing a second radio communicationdevice, which has not been decided as the representative node, totransmit a data packet when receiving the representative nodeadvertisement message; means for allowing the first radio communicationdevice to transmit a confirmation message when receiving the data packetafter transmitting the representative node advertisement message; andmeans for allowing the second radio communication device to stop datapacket transmission during an immediately following active period whenreceiving the confirmation message after transmitting the data packet.6. The radio communication system according to claim 5 furthercomprising: means for allowing the first radio communication device tostop transmission of the representative node advertisement messageduring the immediately following active period when not receiving thedata packet after transmitting the confirmation message or when thenumber of collision detecting time slots is equal to or less than areference value; and means for allowing the second radio communicationdevice to resume data packet transmission during the immediatelyfollowing active period when not receiving the representative nodeadvertisement message after stopping data packet transmission.
 7. Theradio communication system according to claim 5, wherein when therepresentative node is decided, each of the plural radio communicationdevice detects, based on the communication condition in each time slot,such a state that plural radio communication devices are congested, andtransmits, during the immediately following active period, arepresentative node candidate declaration message declaring that theradio communication device becomes a representative node candidate, andeach of plural radio communication devices that have received andtransmitted the representative node candidate declaration messagedecides, based on a predetermined method, one of the plural radiocommunication devices as the representative node.
 8. The radiocommunication system according to claim 7, wherein when the first radiocommunication device decided as the representative node stopstransmission of the representative node advertisement message, priorityof becoming a representative node candidate next time is reduced.
 9. Aradio communication device in a communication system, in which anyperiod within a superframe of a constant cycle is defined as an activeperiod and rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication device to perform time-division two-way communicationusing each time slot, the device comprising: means for detecting, basedon a communication condition in each time slot, such a state that pluralradio communication devices are congested, and deciding one of theplural radio communication device as a representative node; means fortransmitting a representative node advertisement message advertisingthat the radio communication device becomes the representative node whenhaving been decided as the representative node, and transmitting aconfirmation message when receiving a data packet after transmitting therepresentative node advertisement message; and means which, if havingnot been decided as the representative node, transmits a data packetwhen receiving the representative node advertisement message, and stopsdata packet transmission during an immediately following active periodwhen receiving the confirmation message after transmitting the datapacket.
 10. The radio communication device according to claim 9 furthercomprising: means for stopping transmission of the representative nodeadvertisement message during the immediately following active periodwhen not receiving the data packet after transmitting the confirmationmessage or when the number of collision detecting time slots is equal toor less than a reference value; and means for resuming data packettransmission during the immediately following active period when notreceiving the representative node advertisement message aftertransmitting the data packet.
 11. The radio communication deviceaccording to claim 9 wherein when the representative node is decided,such a state that plural radio communication devices are congested isdetected based on a communication condition in each time slot, arepresentative node candidate declaration message declaring that theradio communication device becomes a representative node candidate istransmitted during the immediately following active period, therepresentative node candidate declaration message is received, and basedon a predetermined method, one of the plural radio communication devicesis decided as the representative node.
 12. The radio communicationdevice according to claim 11, wherein when the radio communicationdevice decided as the representative node stops transmission of therepresentative node advertisement message, priority of becoming arepresentative node candidate next time is reduced.
 13. A radiocommunication method, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the methodcomprising: a step of allowing each of the plural radio communicationdevices to detect a collision in each time slot; and a step of allowingeach of the plural radio communication device not only to transmit acollision advertisement message to a predetermined time slot of theplural time slots of an immediately following active period but also toextend the immediately following active period when the radiocommunication device has detected the collision.
 14. A radiocommunication method, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the methodcomprising: a step of allowing each of the plural radio communicationdevice to detect a collision in each time slot; and a step of allowingeach of the plural radio communication device not only to extend acurrent active period but also to transmit a collision advertisementmessage to a predetermined time slot of the current active period whenthe radio communication device has detected the collision.
 15. The radiocommunication method according to claim 13, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 16. The radio communication methodaccording to claim 13, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message.
 17. Aradio communication system, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the systemcomprising: means for allowing each of the plural radio communicationdevice to detect a collision in each time slot; and means for allowingeach of the plural radio communication device not only to transmit acollision advertisement message to a predetermined time slot of theplural time slots of an immediately following active period but also toextend the immediately following active period when the radiocommunication device has detected the collision.
 18. A radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the systemcomprising: means for allowing each of the plural radio communicationdevice to detect a collision in each time slot; and means for allowingeach of the plural radio communication device not only to extend acurrent active period but also to transmit a collision advertisementmessage to a predetermined time slot of the current active period whenthe radio communication device has detected the collision.
 19. The radiocommunication system according to claim 17, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 20. The radio communication systemaccording to claim 17, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message.
 21. Aradio communication device in a radio communication system, in which anyperiod within a superframe of a constant cycle is defined as an activeperiod and rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the device comprising: means for detecting acollision in each time slot; and means for not only transmitting acollision advertisement message to a predetermined time slot of theplural time slots of an immediately following active period but alsoextending the immediately following active period when the radiocommunication device has detected the collision.
 22. A radiocommunication device in a radio communication system, in which anyperiod within a superframe of a constant cycle is defined as an activeperiod and rest is defined as a sleep period, and the active period isdivided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the device comprising: means for detecting acollision in each time slot; and means for not only extending a currentactive period but also transmitting a collision advertisement message toa predetermined time slot of the current active period when the radiocommunication device has detected the collision.
 23. The radiocommunication device according to claim 21, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 24. The radio communication deviceaccording to claim 21, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message.
 25. Aradio communication method, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the methodcomprising: a step of allowing each of the plural radio communicationdevices to transmit a frame including a field of receipt responseinformation on a frame received from another radio communication devicein each of the plural time slots during each time slot period; and astep of allowing each of the plural radio communication devices thathave received the frame to increase or decrease the number of time slotsused by own device during an immediately following superframe periodbased on each piece of receipt response information in the field of thereceipt response information within an immediately preceding superframeperiod.
 26. The radio communication method according to claim 25,wherein when each of the plural radio communication devices was not ableto transmit a frame, own device further transmits, in a frame to betransmitted next, a flag indicating that own device was not able totransmit the frame, and each of the plural radio communication devicesthat have received the frame increases the number of time slots used byown device by the number of flags within the frame.
 27. A radiocommunication system, in which any period within a superframe of aconstant cycle is defined as an active period and rest is defined as asleep period, and the active period is divided into plural time slots toenable each of plural radio communication devices to performtime-division two-way communication using each time slot, the systemcomprising: means for allowing each of the plural radio communicationdevices to transmit a frame including a field of receipt responseinformation on a frame received from another radio communication devicein each of the plural time slots during each time slot period; and meansfor allowing each of the plural radio communication devices that havereceived the frame to increase or decrease the number of time slots usedby own device during an immediately following superframe period based oneach piece of receipt response information in the field of the receiptresponse information within an immediately preceding superframe period.28. The radio communication system according to claim 27, wherein wheneach of the plural radio communication devices was not able to transmita frame, own device further transmits, in a frame to be transmittednext, a flag indicating that own device was not able to transmit theframe, and each of the plural radio communication devices that havereceived the frame increases the number of time slots used by own deviceby the number of flags within the frame.
 29. A radio communicationdevice in a radio communication system, in which any period within asuperframe of a constant cycle is defined as an active period and restis defined as a sleep period, and the active period is divided intoplural time slots to enable each of plural radio communication devicesto perform time-division two-way communication using each time slot, thedevice comprising: means for transmitting a frame including a field ofreceipt response information on a frame received from another radiocommunication device in each of the plural time slots during each timeslot period; and means which, when having received the frame, increasesor decreases the number of time slots used by own device during animmediately following superframe period based on each piece of receiptresponse information in the field of the receipt response informationwithin an immediately preceding superframe period.
 30. The radiocommunication device according to claim 29 further comprising: meanswhich, when own device was not able to transmit a frame, transmits, in aframe to be transmitted next, a flag indicating that own device was notable to transmit the frame, and means which, when having received theframe, increases the number of time slots used by own device by thenumber of flags within the frame.
 31. The radio communication methodaccording to claim 25, wherein when the receipt response informationcontains error information, the number of time slots used is increasedby the number of pieces of error information.
 32. A congestion controlmethod in a radio communication system, in which any period within asuperframe of a constant cycle is defined as an active period and restis defined as a sleep period, and the active period is divided intoplural time slots to enable each of plural radio communication devicesto perform time-division two-way communication using each time slot, themethod comprising: a step of allowing each of the plural radiocommunication devices to transmit a frame including a field of receiptresponse information on a frame received from another radiocommunication device in each of the plural time slots during each timeslot period; and a step of allowing each of the plural radiocommunication devices that have received the frame to determine whetherto stop transmission of own device during an immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within an immediatelypreceding superframe period.
 33. The congestion control method accordingto claim 32, wherein the receipt response information consists ofinformation indicative of “no reception,” “successful reception,” or“error reception,” and in the determination step, it is determinedwhether the total number of pieces of information of “successfulreception” and “error reception” in the field of the receipt responseinformation within the immediately preceding superframe period exceeds afirst threshold value to determine whether to stop transmission of owndevice during the immediately following superframe period.
 34. Thecongestion control method according to claim 32, wherein the receiptresponse information consists of information indicative of “noreception,” “successful reception,” or “error reception,” and in thedetermination step, it is determined whether the number of pieces ofinformation of “successful reception” in the field of the receiptresponse information within the immediately preceding superframe periodexceeds a second threshold value to determine whether to stoptransmission of own device during the immediately following superframeperiod.
 35. The congestion control method according to claim 32, whereinthe receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and in thedetermination step, it is determined whether the number of pieces ofinformation of “successful reception” for a time slot used by the ownnode in the field of the receipt response information within theimmediately preceding superframe period exceeds a third threshold valueto determine whether to stop transmission of own device during theimmediately following superframe period.
 36. The congestion controlmethod according to claim 32, wherein when having stopped transmissionof own node in the determination step, it is determined whether toresume transmission of the own device during the immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within the immediatelypreceding superframe period.
 37. A radio communication system, in whichany period within a superframe of a constant cycle is defined as anactive period and rest is defined as a sleep period, and the activeperiod is divided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the system comprising: means for allowing each ofthe plural radio communication devices to transmit a frame including afield of receipt response information on a frame received from anotherradio communication device in each of the plural time slots during eachtime slot period; and means for allowing each of the plural radiocommunication devices that have received the frame to determine whetherto stop transmission of own device during an immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within an immediatelypreceding superframe period.
 38. The radio communication systemaccording to claim 37, wherein the receipt response information consistsof information indicative of “no reception,” “successful reception,” or“error reception,” and the determination means determines whether thetotal number of pieces of information of “successful reception” and“error reception” in the field of the receipt response informationwithin the immediately preceding superframe period exceeds a firstthreshold value to determine whether to stop transmission of own deviceduring the immediately following superframe period.
 39. The radiocommunication system according to claim 37, wherein the receipt responseinformation consists of information indicative of “no reception,”“successful reception,” or “error reception,” and the determinationmeans determines whether the number of pieces of information of“successful reception” in the field of the receipt response informationwithin the immediately preceding superframe period exceeds a secondthreshold value to determine whether to stop transmission of own deviceduring the immediately following superframe period.
 40. The radiocommunication system according to claim 37, wherein the receipt responseinformation consists of information indicative of “no reception,”“successful reception,” or “error reception,” and the determinationmeans determines whether the number of pieces of information of“successful reception” for a time slot used by own device in the fieldof the receipt response information within the immediately precedingsuperframe period exceeds a third threshold value to determine whetherto stop transmission of own device during the immediately followingsuperframe period.
 41. The radio communication system according to claim37, wherein when having stopped transmission of the own node, thedetermination means determines whether to resume transmission of the owndevice during the immediately following superframe period based on eachpiece of receipt response information in the field of the receiptresponse information within the immediately preceding superframe period.42. A radio communication device in a radio communication system, inwhich any period within a superframe of a constant cycle is defined asan active period and rest is defined as a sleep period, and the activeperiod is divided into plural time slots to enable each of plural radiocommunication devices to perform time-division two-way communicationusing each time slot, the device comprising: means for transmitting aframe including a field of receipt response information on a framereceived from another radio communication device in each of the pluraltime slots during each time slot period; and means which, when havingreceived the frame, determines whether to stop transmission of owndevice during an immediately following superframe period based on eachpiece of receipt response information in the field of the receiptresponse information within an immediately preceding superframe period.43. The radio communication device according to claim 42, wherein thereceipt response information consists of information indicative of “noreception,” “successful reception,” or “error reception,” and thedetermination means determines whether the total number of pieces ofinformation of “successful reception” and “error reception” in the fieldof the receipt response information within the immediately precedingsuperframe period exceeds a first threshold value to determine whetherto stop transmission of own device during the immediately followingsuperframe period.
 44. The radio communication device according to claim42, wherein the receipt response information consists of informationindicative of “no reception,” “successful reception,” or “errorreception,” and the determination means determines whether the number ofpieces of information of “successful reception” in the field of thereceipt response information within the immediately preceding superframeperiod exceeds a second threshold value to determine whether to stoptransmission of own device during the immediately following superframeperiod.
 45. The radio communication device according to claim 42,wherein the receipt response information consists of informationindicative of “no reception,” “successful reception,” or “errorreception,” and the determination means determines whether the number ofpieces of information of “successful reception” for a time slot used byown node in the field of the receipt response information within theimmediately preceding superframe period exceeds a third threshold valueto determine whether to stop transmission of own device during theimmediately following superframe period.
 46. The radio communicationdevice according to claim 42, wherein when having stopped transmissionof own device, the determination means determines whether to resumetransmission of the own device during the immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within the immediatelypreceding superframe period.
 47. The radio communication methodaccording to claim 2, wherein when the representative node is decided,each of the plural radio communication device detects, based on thecommunication condition in each time slot, such a state that pluralradio communication devices are congested, and transmits, during theimmediately following active period, a representative node candidatedeclaration message declaring that the radio communication devicebecomes a representative node candidate, and each of plural radiocommunication devices that have received and transmitted therepresentative node candidate declaration message decides, based on apredetermined method, one of the plural radio communication devices asthe representative node.
 48. The radio communication method according toclaim 47, wherein when the first radio communication device decided asthe representative node stops transmission of the representative nodeadvertisement message, priority of becoming a representative nodecandidate next time is reduced.
 49. The radio communication systemaccording to claim 6, wherein when the representative node is decided,each of the plural radio communication device detects, based on thecommunication condition in each time slot, such a state that pluralradio communication devices are congested, and transmits, during theimmediately following active period, a representative node candidatedeclaration message declaring that the radio communication devicebecomes a representative node candidate, and each of plural radiocommunication devices that have received and transmitted therepresentative node candidate declaration message decides, based on apredetermined method, one of the plural radio communication devices asthe representative node.
 50. The radio communication system according toclaim 49, wherein when the first radio communication device decided asthe representative node stops transmission of the representative nodeadvertisement message, priority of becoming a representative nodecandidate next time is reduced.
 51. The radio communication deviceaccording to claim 10, wherein when the representative node is decided,such a state that plural radio communication devices are congested isdetected based on a communication condition in each time slot, arepresentative node candidate declaration message declaring that theradio communication device becomes a representative node candidate istransmitted during the immediately following active period, therepresentative node candidate declaration message is received, and basedon a predetermined method, one of the plural radio communication devicesis decided as the representative node.
 52. The radio communicationdevice according to claim 51, wherein when the radio communicationdevice decided as the representative node stops transmission of therepresentative node advertisement message, priority of becoming arepresentative node candidate next time is reduced.
 53. The radiocommunication method according to claim 14, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 54. The radio communication methodaccording to claim 14, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message. 55.The radio communication system according to claim 18, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 56. The radio communication systemaccording to claim 18, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message. 57.The radio communication device according to claim 22, wherein the radiocommunication device that has detected the collision transmits thecollision advertisement message together with data to another time slotfor transmitting the data during the current active period as well as tothe predetermined time slot.
 58. The radio communication deviceaccording to claim 22, wherein the collision advertisement messageincludes time slot identification information indicative of the timeslot that has detected the collision, and each of the plural radiocommunication devices that has received the collision advertisementmessage stops next transmission when a time slot transmitted by theradio communication device last time does not match the time slotidentification information in the collision advertisement message. 59.The congestion control method according to claim 33, wherein the receiptresponse information consists of information indicative of “noreception,” “successful reception,” or “error reception,” and in thedetermination step, it is determined whether the number of pieces ofinformation of “successful reception” in the field of the receiptresponse information within the immediately preceding superframe periodexceeds a second threshold value to determine whether to stoptransmission of own device during the immediately following superframeperiod.
 60. The congestion control method according to claim 33, whereinthe receipt response information consists of information indicative of“no reception,” “successful reception,” or “error reception,” and in thedetermination step, it is determined whether the number of pieces ofinformation of “successful reception” for a time slot used by the ownnode in the field of the receipt response information within theimmediately preceding superframe period exceeds a third threshold valueto determine whether to stop transmission of own device during theimmediately following superframe period.
 61. The congestion controlmethod according to claim 33, wherein when having stopped transmissionof own node in the determination step, it is determined whether toresume transmission of the own device during the immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within the immediatelypreceding superframe period.
 62. The radio communication systemaccording to claim 38, wherein the receipt response information consistsof information indicative of “no reception,” “successful reception,” or“error reception,” and the determination means determines whether thenumber of pieces of information of “successful reception” in the fieldof the receipt response information within the immediately precedingsuperframe period exceeds a second threshold value to determine whetherto stop transmission of own device during the immediately followingsuperframe period.
 63. The radio communication system according to claim38, wherein the receipt response information consists of informationindicative of “no reception,” “successful reception,” or “errorreception,” and the determination means determines whether the number ofpieces of information of “successful reception” for a time slot used byown device in the field of the receipt response information within theimmediately preceding superframe period exceeds a third threshold valueto determine whether to stop transmission of own device during theimmediately following superframe period.
 64. The radio communicationsystem according to claim 38, wherein when having stopped transmissionof the own node, the determination means determines whether to resumetransmission of the own device during the immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within the immediatelypreceding superframe period.
 65. The radio communication deviceaccording to claim 43, wherein the receipt response information consistsof information indicative of “no reception,” “successful reception,” or“error reception,” and the determination means determines whether thenumber of pieces of information of “successful reception” in the fieldof the receipt response information within the immediately precedingsuperframe period exceeds a second threshold value to determine whetherto stop transmission of own device during the immediately followingsuperframe period.
 66. The radio communication device according to claim43, wherein the receipt response information consists of informationindicative of “no reception,” “successful reception,” or “errorreception,” and the determination means determines whether the number ofpieces of information of “successful reception” for a time slot used byown node in the field of the receipt response information within theimmediately preceding superframe period exceeds a third threshold valueto determine whether to stop transmission of own device during theimmediately following superframe period.
 67. The radio communicationdevice according to claim 43, wherein when having stopped transmissionof own device, the determination means determines whether to resumetransmission of the own device during the immediately followingsuperframe period based on each piece of receipt response information inthe field of the receipt response information within the immediatelypreceding superframe period.